Systems and methods for making encapsulated hourglass shaped stents

ABSTRACT

Systems and methods for the manufacture of an hourglass shaped stent-graft assembly comprising an hourglass shaped stent, graft layers, and an assembly mandrel having an hourglass shaped mandrel portion. Hourglass shaped stent may have superelastic and self-expanding properties. Hourglass shaped stent may be encapsulated using hourglass shaped mandrel assembly coupled to a dilation mandrel used for depositing graft layers upon hourglass shaped mandrel assembly. Hourglass shaped mandrel assembly may have removably coupled conical portions. The stent-graft assembly may be compressed and heated to form a monolithic layer of biocompatible material. Encapsulated hourglass shaped stents may be used to treat subjects suffering from heart failure by implanting the encapsulated stent securely in the atrial septum to allow blood flow from the left atrium to the right atrium when blood pressure in the left atrium exceeds that on the right atrium. The encapsulated stents may also be used to treat pulmonary hypertension.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part patent application of U.S.patent application Ser. No. 15/798,250, filed Oct. 30, 2017, which is acontinuation application of U.S. patent application Ser. No. 15/608,948,filed May 30, 2017, which claims priority to U.S. Provisional PatentApplication Ser. No. 62/343,658, filed May 31, 2016, the entire contentsof each of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This application relates to systems and methods for the manufacture ofencapsulated stents for treating congestive heart failure and otherdisorders treated with encapsulated stents.

BACKGROUND

Heart failure is the physiological state in which cardiac output isinsufficient to meet the needs of the body and the lungs. CongestiveHeart Failure (CHF) occurs when cardiac output is relatively low due toreduced contractility or heart muscle thickening or stiffness. There aremany possible underlying causes of CHF, including myocardial infarction,coronary artery disease, valvular disease, and myocarditis.

CHF is associated with neurohormonal activation and alterations inautonomic control. Although these compensatory neurohormonal mechanismsprovide valuable support for the heart under normal physiologicalcircumstances, they also have a fundamental role in the development andsubsequent progression of CHF. For example, one of the body's maincompensatory mechanisms for reduced blood flow in CHF is to increase theamount of salt and water retained by the kidneys. Retaining salt andwater, instead of excreting it into the urine, increases the volume ofblood in the bloodstream and helps to maintain blood pressure. However,the larger volume of blood also stretches the heart muscle, enlargingthe heart chambers, particularly the ventricles. At a certain amount ofstretching, the hearts contractions become weakened, and the heartfailure worsens. Another compensatory mechanism is vasoconstriction ofthe arterial system. This mechanism, like salt and water retention,raises the blood pressure to help maintain adequate perfusion.

In low ejection fraction (EF) heart failure, high pressures in the heartresult from the body's attempt to maintain the high pressures needed foradequate peripheral perfusion. However, the heart weakens as a result ofthe high pressures, aggravating the disorder. Pressure in the leftatrium may exceed 25 mmHg, at which stage, fluids from the blood flowingthrough the pulmonary circulatory system flow out of the interstitialspaces and into the alveoli, causing pulmonary edema and lungcongestion.

CHF is generally classified as either Heart Failure with reducedEjection Fraction (HFrEF) or Heart Failure with preserved EjectionFraction (HFpEF). In HFrEF, the pumping action of the heart is reducedor weakened. A common clinical measurement is the ejection fraction,which is a function of the blood ejected out of the left ventricle(stroke volume), divided by the maximum volume remaining in the leftventricle at the end of diastole or relaxation phase (End DiastolicVolume). A normal ejection fraction is greater than 50%. HFrEF has adecreased ejection fraction of less than 40%. A patient with HFrEF mayusually have a larger left ventricle because of a phenomenon calledcardiac remodeling that occurs secondarily to the higher ventricularpressures.

In HFpEF, the heart generally contracts normally, with a normal ejectionfraction, but is stiffer, or less compliant, than a healthy heart wouldbe when relaxing and filling with blood. This stiffness may impede bloodfrom filling the heart, and produce backup into the lungs, which mayresult in pulmonary venous hypertension and lung edema. HFpEF is morecommon in patients older than 75 years, especially in women with highblood pressure.

Both variants of CHF have been treated using pharmacological approaches,which typically involve the use of vasodilators for reducing theworkload of the heart by reducing systemic vascular resistance, as wellas diuretics, which inhibit fluid accumulation and edema formation, andreduce cardiac filling pressure. However, pharmacological approaches arenot always successful, as some people may be resistant or experiencesignificant side effects

In more severe cases of CHF, assist devices such as mechanical pumpshave been used to reduce the load on the heart by performing all or partof the pumping function normally done by the heart. Chronic leftventricular assist devices (LVAD), and cardiac transplantation, oftenare used as measures of last resort. However, such assist devices aretypically intended to improve the pumping capacity of the heart, toincrease cardiac output to levels compatible with normal life, and tosustain the patient until a donor heart for transplantation becomesavailable. Such mechanical devices enable propulsion of significantvolumes of blood (liters/min), but are limited by a need for a powersupply, relatively large pumps, and the risk of hemolysis, thrombusformation, and infection. In addition to assist devices, surgicalapproaches such as dynamic cardiomyoplasty or the Batista partial leftventriculectomy may also be used in severe cases. However theseapproaches are highly invasive and have the general risks associatedwith highly invasive surgical procedures.

U.S. Pat. No. 6,468,303 to Amplatz et al. describes a collapsiblemedical device and associated method for shunting selected organs andvessels. Amplatz describes that the device may be suitable to shunt aseptal defect of a patient's heart, for example, by creating a shunt inthe atrial septum of a neonate with hypoplastic left heart syndrome(HLHS). Amplatz describes that increasing mixing of pulmonary andsystemic venous blood improves oxygen saturation. Amplatz describes thatdepending on the hemodynamics, the shunting passage can later be closedby an occluding device. However, Amplatz is silent on the treatment ofCHF or the reduction of left atrial pressure, and is also silent onmeans for regulating the rate of blood flow through the device.

U.S. Pat. No. 8,070,708 to Rottenberg describes a method and device forcontrolling in-vivo pressure in the body, and in particular, the heart.The device described in Rottenberg involves a shunt to be positionedbetween two or more lumens in the body to permit fluid to flow betweenthe two lumens. The Rottenberg patent further describes that anadjustable regulation mechanism may be configured to cover an opening ofthe shunt to regulate flow between the two lumens. The shunt isconfigured such that the flow permitted is related to a pressuredifference between the two lumens. The adjustable regulation mechanismmay be remotely activated. The Rottenberg patent describes that thedevice described may be used to treat CHF by controlling pressuredifference between the left atrium and the right atrium. WhileRottenberg describes a mechanism for treating CHF by controlling theflow between the left atrium and the right atrium, it does not describethe encapsulation of an hourglass shaped stent.

U.S. Patent Publication No. 2005/0165344 to Dobak, III describes anapparatus for treating heart failure that includes a conduit positionedin a hole in the atrial septum of the heart, to allow flow from the leftatrium into the right atrium. Dobak describes that the shunting of bloodwill reduce left atrial pressures, thereby preventing pulmonary edemaand progressive left ventricular dysfunction, and reducing LVEDP. Dobakdescribes that the conduit may include a self-expandable tube withretention struts, such as metallic arms that exert a slight force on theatrial septum on both sides and pinch or clamp the valve to the septum,and a one-way valve member, such as a tilting disk, bileaflet design, ora flap valve formed of fixed animal pericardial tissue. However, Dobakstates that a valved design may not be optimal due to a risk of bloodstasis and thrombus formation on the valve, and that valves can alsodamage blood components due to turbulent flow effects. Dobak does notprovide any specific guidance on how to avoid such problems.

U.S. Pat. No. 9,034,034 to Nitzan, incorporated herein by reference,describes a device for regulating blood pressure between a patient'sleft atrium and right atrium which comprises an hourglass-shaped stenthaving a neck region and first and second flared regions, the neckregion disposed between the first and second end regions and configuredto engage the fossa ovalis of the patient's atrial septum. Nitzandescribes that the hourglass shaped stent is also encapsulated with abiocompatible material. While Nitzan describes a method for themanufacture of an hourglass shaped stent for the treatment of CHF,Nitzan is silent on the method of encapsulating the stent.

U.S. Pat. No. 6,214,039 to Banas, incorporated herein by reference,describes a method for covering a radially endoluminal stent. In themethod described by Banas, the encapsulated stent is assembled byjoining a dilation mandrel and a stent mandrel, placing the graft on thedilation mandrel where it is radially expanded, and passing the expandedgraft over the stent that is positioned on the stent mandrel. WhileBanas describes a method for encapsulating a cylindrical stent, themethod in Banas does not describe encapsulation of an hourglass shapedstent intended for treatment of CHF. The method for assembling thecovered stent and mandrel assembly described in Banas would beinappropriate for assembly of an hourglass stent described in Nitzan.

U.S. Pat. No. 6,797,217 to McCrea, incorporated herein by reference,describes a method for encapsulating stent-grafts. McCrea describesmethods for encapsulating an endoluminal stent fabricated from a shapememory alloy. The Method described by McCrea involves an endoluminalstent encapsulated in an ePTFE covering which circumferentially coversboth the luminal and abluminal walls along at least a portion of thelongitudinal extent of the endoluminal stent. McCrea further describesapplying pressure to the stent-graft assembly and heating the assemblyto complete the encapsulation. While McCrea describes an encapsulatedendoluminal stent, it does not describe the encapsulation of anhourglass shaped stent for the treatment of CHF.

In view of the above-noted drawbacks of previously known systems, itwould be desirable to provide systems and methods of manufacture ofencapsulated hourglass shaped stents for treating congestive heartfailure and other disorders treated with hourglass shaped stent-graftassemblies.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of previously-knownsystems and methods by providing systems and methods for makingencapsulated hourglass shaped stents for treating CHF and otherconditions benefited by encapsulated hourglass shaped stents such aspulmonary hypertension. The hourglass or “diabolo” shaped stents areconfigured to be encapsulated using a mandrel assembly.

In accordance with one aspect, a method for making an encapsulatedstent-graft may involve, providing a mandrel having a first conicalregion with a first apex and a second conical region with a second apex,placing an expandable stent having an hourglass shape in an expandedform on the mandrel so that a first flared region of the expandablestent conforms to the first conical region and a second flared region ofthe expandable stent conforms to the second conical region, associatinga biocompatible material with the expandable stent to form a stent-graftassembly, and compressing the stent-graft assembly against the mandrelto form the encapsulated stent-graft. The first conical region and thesecond conical region may be aligned so that the first and second apexescontact one another.

The biocompatible material may have first and second ends andassociating the biocompatible material with the expandable stentinvolves placing the biocompatible material within a lumen of theexpandable stent. The method may further include placing a secondbiocompatible material over the expandable stent. Compressing thestent-graft assembly may involve winding a layer of tape over thebiocompatible material to compress the stent-graft assembly against themandrel. The expandable stent may include through-wall openings, and themethod may further involve heating the stent-graft assembly to cause thebiocompatible material and the second biocompatible material to bond toone another through the through-wall openings. Heating the stent-graftassembly may cause the biocompatible material and the secondbiocompatible material to become sintered together to form a monolithiclayer of biocompatible material. The method may further involve applyinga layer of Fluorinated Ethylene Propylene (FEP) to biocompatiblematerial or second biocompatible material. The biocompatible materialmay be pre-formed. The method may further involve manipulating theencapsulated stent-graft to a compressed shape and loading theencapsulated stent-graft into a delivery sheath. A first end diameter ofthe expandable stent may be different in size from a second enddiameter. The mandrel may have a neck region disposed between a firstconical region and a second conical region and the mandrel may beconfigured to be removably uncoupled at the neck region into a firsthalf having at least the first conical region and a second half havingat least the second conical region.

In accordance with another aspect, a method for making an encapsulatedstent-graft may involve providing a mandrel assembly having anasymmetric shape, providing an expandable stent in an expanded form,coupling a biocompatible material to the expandable stent to form astent-graft assembly, and compressing the stent-graft assembly on themandrel assembly to form the encapsulated stent-graft. The expandablestent may be configured to conform to the asymmetric shape formed by themandrel assembly.

The expandable stent and the biocompatible material may be coupled onthe mandrel assembly or before placement on the mandrel assembly. Themethod may further involve coupling a second biocompatible material toan opposing surface of the expandable stent to form the stent-graftassembly. The second biocompatible material may be formed of a same ordifferent material as the biocompatible material. The mandrel assemblymay include a first mandrel and a second mandrel, and the method mayfurther involve, positioning the first mandrel within the first end ofthe expandable stent such that a portion of the second biocompatiblematerial is positioned between the first mandrel and the expandablestent, and positioning the second mandrel within the second end of theexpandable stent such that a portion of the second biocompatiblematerial is positioned between the second mandrel and the expandablestent. The biocompatible material may be a pre-formed biocompatiblegraft layer having the shape of the expandable stent. The pre-formedbiocompatible graft layer may engage the expandable stent on the mandrelassembly.

In accordance with yet another aspect, a method for making anencapsulated stent-graft may involve providing an asymmetrical stent,placing a first biocompatible material over the asymmetrical stent,providing a second biocompatible material for placement within theasymmetrical stent, inserting a balloon catheter having an inflatableballoon within the asymmetrical stent in a deflated state such that thesecond biocompatible material is between the asymmetrical stent and theinflatable balloon, and inflating the inflatable balloon to an inflatedstate conforming to the shape of the asymmetrical stent, thereby causingthe second biocompatible material to engage with the asymmetrical stentto form the encapsulated stent-graft.

The method may further involve controlling the pressure within theballoon to achieve a desired adhesion between the first biocompatiblematerial and the second biocompatible material. The method may furtherinvolve controlling the pressure within the balloon to achieve a desiredinter-nodal-distance of the graft material. The second biocompatiblematerial may be placed within the asymmetrical stent prior to insertingthe balloon catheter within the asymmetrical stent. The secondbiocompatible material may be disposed on the inflatable balloon, andinflating the inflatable balloon may cause the second biocompatiblematerial disposed on the inflatable balloon to contact and inner surfaceof the asymmetrical stent thereby engaging the second biocompatiblematerial with the asymmetrical stent.

In accordance with yet another aspect, a method for making anencapsulated stent-graft may involve providing a funnel having a largeend and a small end, placing an asymmetric stent with a first end, asecond end, an exterior surface and an interior surface within the largeend of the funnel, placing a biocompatible tube over the small end ofthe funnel, the biocompatible tube having a stent receiving portion anda remaining portion, advancing the asymmetric stent through the funneland out the small end of the funnel, thereby depositing the asymmetricstent into the biocompatible tube such that the stent is positionedwithin the stent receiving portion of the biocompatible tube, therebyengaging an exterior surface of the asymmetric stent with thebiocompatible tube, pulling the remaining portion of the biocompatibletube through the first end of the asymmetric stent and out the secondend, introducing a first mandrel having a shape similar to the firstside of the asymmetric stent into the first side of asymmetric stentthereby engaging the interior surface of the first side of theasymmetric stent with a portion of the remaining portion of thebiocompatible tube, and introducing a second mandrel having a shapesimilar to the second side of the asymmetric stent into the second sideof the asymmetric stent thereby engaging the interior surface of thesecond side of the asymmetric stent with a portion of the remainingportion of the biocompatible tube.

In accordance with yet another aspect, an hourglass shaped mandrelassembly for making an encapsulated stent-graft may involve a firstportion having at least a first conical region having a flared end witha first diameter and an apex end with a second diameter, a secondportion having at least a second conical region having a flared end withthird diameter and an apex end with a fourth diameter, and a taperedregion coupled to the flared end of the first portion and extending awayfrom the flared end of the first portion. The tapered region may have aflared end with a fifth diameter and a tapered end with a sixth diametersuch that the fifth diameter is equal to the first diameter and thesixth diameter is smaller than the fifth diameter. The first conicalregion of the first portion and the second conical region of the secondportion may be aligned so that apexes of the first portion and secondportion are contacting one another. The hourglass shaped mandrelassembly may further include a neck region positioned between the apexend of the first portion and the apex end of the second portion suchthat the neck region is affixed to at least the first portion or thesecond portion. The first portion and the second portion may beremovably coupled at the apex end of the first portion and the apex endof the second portion. The hourglass shaped mandrel may be configured toexpand radially.

In accordance with yet another aspect, a method for making anencapsulated stent-graft may involve providing a stent having a firstflared region, a second flared region and a neck region therebetween.The stent may be compressed and the second flared region and neck regionmay be placed within a graft tube and permitted to expand depositing afirst portion of graft tube on the second flared region and neck region.The graft tube may be guided through the interior of the stent such thatit extends beyond the first flared region, depositing a second portionof graft material upon the interior of the stent. A first mandrelportion having a similar shape as the first flared portion but withslightly smaller dimensions may be placed within the first flared regionwhile simultaneously positioning the second end of the graft tube overthe first mandrel portion. A second mandrel portion having a similarshape as the second flared region but with slightly smaller dimensionsmay be placed within the second flared region. A second end of the grafttube may be separated from the first mandrel portion and positioned overthe first flared region and neck region to deposit a third portion ofgraft tube over the first flared region and neck region of the stent,resulting a stent-graft assembly. A flexible sleeve having a similarsize and shape to the stent-graft assembly and a longitudinal openingmay be positioned around the stent-graft assembly. A compressor havingtwo halves and an indentation having a similar size and shape as theflexible sleeve covering the stent-graft assembly may be coupled to theflexible sleeve to compresses the stent-graft assembly against themandrel. Heat may be applied to the resulting assembly to createmonolithic layer of biocompatible material and ultimately generate anencapsulated stent.

In accordance with yet another aspect, a stent-graft assembly mayinvolve an expandable stent having an exterior, a lumen and a firstlength that includes a first region and first end, a second region and asecond end, and a middle region positioned between the first region andthe second region. The stent-graft assembly may further involve abiocompatible graft-tube having a second length greater than twice thefirst length of the stent. The second length of the biocompatiblegraft-tube may have first, second, and third portions. The first portionmay extend through the lumen from the first end of the first region,through the middle region and to the second end of the second region.The second portion may be continuously joined to the first portion atthe first end and extend along the exterior of the stent from the firstend and into the middle region. The third portion may be continuouslyjoined to the second portion at the second end and extend along theexterior of the second region and into the middle region. In thismanner, the second and third portions may overlap and may be joined toone another in the middle region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side view of hourglass shaped stent constructed in accordancewith the methods of the present invention.

FIG. 2 is a cross-section view of hourglass shaped stent encapsulatedwith first and second graft layers.

FIG. 3 is a partially exploded side view of assembly apparatus formanufacturing hourglass stent-graft assembly in accordance with themethods of the present invention.

FIG. 4 is a side view of hourglass shaped mandrel assembly section ofassembly apparatus for manufacturing hourglass shaped stent-graftassembly in accordance with the methods of the present invention.

FIG. 5 is a side view of assembly apparatus engaged with first grafttube at the tapered region.

FIG. 6 is a side view of assembly apparatus engaged with first grafttube over hourglass shaped mandrel assembly section.

FIG. 7 is a side view of first graft layer disposed over hourglassshaped mandrel assembly section of assembly apparatus.

FIGS. 8A-8C are side views of assembly apparatus engaged with firstgraft layer and hourglass shaped stent.

FIG. 9 is a side view of assembly apparatus engaged with second grafttube at the tapered region.

FIG. 10 is a side view of assembly apparatus engaged with second grafttube over hourglass shaped mandrel assembly section of assemblyapparatus.

FIG. 11 is a side view of stent-graft disposed over hourglass shapedmandrel assembly section.

FIGS. 12A-12D are side views sequentially illustrating an encapsulationtechnique which includes deploying the stent into a sleeve of graftmaterial, and involving a male and female mandrel.

FIGS. 13A-13E are side views sequentially illustrating an encapsulationtechnique involving pre-shaped grafts and a male and female mandrel.

FIGS. 14A-14D are side views sequentially illustrating an encapsulationtechnique involving an inflatable balloon.

FIGS. 15A-15F are side views sequentially illustrating an encapsulationtechnique involving a funnel, a single graft material sleeve, and a maleand female mandrel.

FIGS. 16A-16D illustrate the structure of the stent-graft assemblyhaving two and three layer regions.

FIGS. 17A-17E are side views sequentially illustrating a technique ofdepositing a first graft portion on a stent.

FIGS. 18A-18B are side views sequentially illustrating a technique ofdepositing a second graft portion on a stent.

FIGS. 19A-19B illustrates the mandrel assembly including the firstmandrel portion illustrated in FIG. 19A and the second mandrel portionillustrated in FIG. 19B.

FIGS. 20A-20C are side views and a close-up view illustrating atechnique of depositing a third graft portion on a stent.

FIGS. 21A-21B illustrate a perspective view of the flexible sleeve and aside view of the flexible sleeve mounted on the stent-graft assembly.

FIGS. 22A-22B illustrate a perspective view of a compression shell and aside view of the flexible sleeve mounted on the flexible sleeve andstent-graft assembly.

FIGS. 23A-23C illustrate images of an encapsulated stent generated usingthe approaching shown in FIGS. 17A-22B implanted in an animal subject.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to systems and methodsfor the manufacture of hourglass or “diabolo” shaped stents encapsulatedwith biocompatible material for treating subjects suffering fromcongestive heart failure (CHF) or alternatively pulmonary hypertension.The hourglass or “diabolo” shaped stents are configured to beencapsulated using an hourglass shaped mandrel assembly having adilation portion and two conical regions that may be removably coupled.The hourglass shaped stents may be specifically configured to be lodgedsecurely in the atrial septum, preferably the fossa ovalis, to allowblood flow from the left atrium to the right when blood pressure in theleft atrium exceeds that on the right atrium. The resulting encapsulatedstents are particularly useful for the purpose of inter-atrial shuntingas they provide long-term patency and prevent tissue ingrowth within thelumen of the encapsulated stent. However, it is understood that thesystems and methods described herein may also be applicable to otherconditions benefited from an encapsulated hourglass shaped stent such aspulmonary hypertension wherein the encapsulated hourglass shaped stentis used as a right-to-left shunt.

Referring now to FIG. 1, stent 110 is illustrated. Stent 110 ishourglass or “diabolo” shaped and may be radially expandable to anexpanded state and/or compressible to a compressed state. Stent 110 maybe self-expandable or may be manually expandable. For example, stent 110may be transitioned from a compressed state to an expanded state using aballoon expandable. Stent 110 has three general regions: first flaredregion 102, second flared region 106, and neck region 104 disposedbetween the first and second flared regions. First flared region 102 hasfirst end region diameter D1, second flared region 106 has second endregion diameter D2, and neck region 104 has neck diameter D3. As shownin FIG. 1, neck region 104 of stent 110 is significantly narrower thanfirst flared region 102 and second flared region 106. Also shown in FIG.1, stent 110 may be asymmetric. For example, stent 110 may be asymmetricto take advantage of the natural features of the atrial septum of theheart as well as the left and right atrium cavities. Alternatively,hourglass shaped stent 110 may be symmetric with the first end regiondiameter D1 being equal to the second end region diameter D2. Firstflared region 102 and second flared region 106 also may have eitherstraight or curved profiles or both. For example, strut 111 has astraight profile and strut 108 has a curved profile. Additionally, firstflared region 102 and second flared region 106 may assume any angularposition consistent with the hour-glass configuration.

Stent 110 is preferably comprised of a self-expanding material havingsuperelastic properties. For example, a shape-memory metal such asnickel titanium (NiTi), also known as NITINOL may be used. Othersuitable materials known in the art of deformable stents forpercutaneous implantation may alternatively be used such as other shapememory alloys, self-expanding materials, superelastic materials,polymers, and the like. The tube may be laser-cut to define a pluralityof struts and connecting members. For example, as illustrated in FIG. 1,the tube may be laser-cut to define a plurality of sinusoidal ringsconnected by longitudinally extending struts. Struts 108 and 111 andsinusoidal rings 112-116 illustrated in FIG. 1 may be laser cut to forman integral piece of unitary construction. Alternatively, struts 111 andsinusoidal rings 112-116 may be separately defined to form differentpieces of shape-memory metal and subsequently coupled together to formstent 110. The stent may also be electropolished to reducethrombogenicity.

Stent 110 may be expanded on a mandrel to define first flared region102, second flared region 106, and neck region 104. The expanded stentthen may be heated to set the shape of stent 110. The stent may beexpanded on a mandrel in accordance with the teachings of U.S. Pat. No.9,034,034 to Nitzan and may take the form of a stent described in thatpatent, U.S. Pat. No. 9,707,382 to Nitzan, and/or U.S. Pat. No.10,076,403 to Eigler, the entire contents of each of which areincorporated by reference herein. In one example, stent 110 is formedfrom a tube of NITINOL, shaped using a shape mandrel, and placed into anoven for 11 minutes at 530° C. to set the shape. The mandrel disclosedin FIGS. 3-4 may be configured as a shaping mandrel to set the shape ofstent 110 or, alternatively, a different mandrel may be used as theshaping mandrel.

Referring now to FIG. 2, stent 110 is at least partially covered withbiocompatible material, as shown in FIG. 2, to create stent-graftassembly 120. Biocompatible material may be expandedpolytetrafluoroethylene (ePTFE), silicone, polycarbonate urethane,DACRON (polyethylene terephthalate), Ultra High Molecular WeightPolyethylene (UHMWPE), or polyurethane, or of a natural material such aspericardial tissue, e.g., from an equine, bovine, or porcine source orhuman tissue such as human placenta or other human tissues. Thebiocompatible material is preferably smooth so as to inhibit thrombusformation, and optionally may be impregnated with carbon so as topromote tissue ingrowth. Alternatively, to promote tissue ingrowth andendothelization, the biocompatible material may form a mesh-likestructure. The biocompatible material may be pre-shaped using adedicated pre-shaping mandrel and heat treatment to simplify themounting of the biocompatible material on an encapsulation mandrel, asdiscussed in detail below. Pre-shaping the biocompatible material hasbeen shown to simplify the handling and mounting of the biocompatiblematerial on the mandrel, thereby reducing stretching and the risk fortears in the biocompatible material and may be especially beneficial forencapsulating asymmetrical stents. Portions of stent 110 such as firstflared region 102 may not be covered with the biocompatible material.

Generally, the stent is positioned between a first and second layer ofgraft material by covering inner surface 121 of stent 110 with firstgraft layer 170, and covering outer surface 123 of stent 110 with secondgraft layer 190. First graft layer 170 and second graft layer 190 eachmay have a first end and a second end and may have lengths that areabout equal. Alternatively, first graft layer 170 and second graft layer190 may have different lengths. Stent 110 may have a length that isshorter than the length of first graft layer 170 and second graft layer190. In other embodiments, stent 110 may have a length that is longerthan the length of first graft layer 170 and/or second graft layer 190.As discussed in detail below, two or more graft layers may cover thestent or portions of the stent. As also discussed below, the graftlayers may be securely bonded together to form a monolithic layer ofbiocompatible material. For example, first and second graft tubes may besintered together to form a strong, smooth, substantially continuouscoating that covers the inner and outer surfaces of the stent. Portionsof the coating then may be removed as desired from selected portions ofthe stent using laser-cutting or mechanical cutting, for example.

In a preferred embodiment, stent 110 is encapsulated with ePTFE. It willbe understood by those skilled in the art that ePTFE materials have acharacteristic microstructure consisting of nodes and fibrils, with thefibrils orientation being substantially parallel to the axis oflongitudinal expansion. Expanded polytetrafluoroethylene materials aremade by ram extruding a compressed billet of particulatepolytetrafluoroethylene and extrusion lubricant through an extrusion dieto form sheet or tubular extrudates. The extrudate is thenlongitudinally expanded to form the node-fibril microstructure andheated to a temperature at or above the crystalline melt point ofpolytetrafluoroethylene, i.e., 327° C., for a period of time sufficientto sinter the ePTFE material. Heating may take place in a vacuum chamberto prevent oxidation of the stent. Alternatively, heating may take placein a nitrogen rich environment. A furnace may be used to heat thestent-graft assembly. Alternatively, or in addition to, the mandrel uponwhich the stent-graft assembly rests may be a heat source used to heatthe stent-graft assembly.

FIGS. 3-11 generally illustrate one method of making stent-graftassembly 120, as depicted in FIGS. 1-2. FIG. 3 is a partially explodedview of assembly apparatus 130. Assembly apparatus 130 may comprisetapered dilation mandrel 131, stent retaining mandrel 134 and stentenclosing mandrel 138. Tapered dilation mandrel 131 comprises first end132 having a tapered diameter and second end 133 wherein the diameter ofsecond end 133 is greater than the tapered diameter. Where othertechniques are used to dilate stent 110 and biocompatible graftmaterial, tapered dilation mandrel 131 may not be necessary and thusassembly apparatus 130 may comprise stent retaining mandrel 134 andstent enclosing mandrel 138.

Stent retaining mandrel 134 may be permanently affixed to second end 133of tapered dilation mandrel 131 or alternatively may be removablycoupled to tapered dilation mandrel. For example, stent retainingmandrel 134 may be screwed into tapered dilation mandrel 131 using ascrew extending from stent retaining mandrel 134 and a threaded insertembedded into tapered dilation mandrel 131. However, it will beunderstood by those in the art that couplings are interchangeable andmay be any of a wide variety of suitable couplings.

Stent retaining mandrel 134 may comprise a conical region defined bylarge diameter end 135 and an apex end 136. Large diameter end 135 maybe equal in diameter with second end 133 of tapered dilation mandrel131, and larger in diameter than apex end 136. It is understood thatstent retaining mandrel 134 may alternatively be other shapes includingnon-conical shapes. Stent retaining mandrel 134 may optionallyincorporate neck region 137. Neck region 137 may extend from apex end136, as shown in FIG. 3, and may have the same diameter as apex end 136.Alternatively, neck region 137 may extend from stent enclosing mandrel138.

Stent enclosing mandrel 138 is removably coupled to stent retainingmandrel 134. For example, stent enclosing mandrel 138 may be screwedinto stent retaining mandrel 134 using screw 139 extending from stentenclosing mandrel 138 and threaded insert 140 embedded into stentretaining mandrel 134. Alternatively, screw 139 may extend from stentretaining mandrel 134 and threaded insert may be embedded into stentenclosing mandrel 138. While the figures depict threaded coupling, itwill be understood by those skilled in the art that the couplings areinterchangeable and may be any of a wide variety of suitable couplings.In another example, stent retaining mandrel 134 may be a female mandrelhaving a receiving portion and stent enclosing mandrel 138 may be a malemandrel having a protruding portion. However, it is understood thatstent retaining mandrel 134 may be a male mandrel having a protrudingportion and stent enclosing mandrel 138 may be a female mandrel having areceiving portion.

Stent enclosing mandrel 138 may comprise a conical region defined bylarge diameter end 142 and an apex end 141, wherein large diameter end142 is larger in diameter than apex end 141. It is understood that stentenclosing mandrel 138 alternatively take other shapes includingnon-conical shapes. Stent enclosing mandrel 138 may be permanentlyaffixed to handle segment 144 at large diameter end 142. Alternatively,stent enclosing mandrel 138 may be removably coupled to handle segment144. Where stent enclosing mandrel 138 is removably coupled to handlesegment 144, handle segment 144 may be removed and replaced with atapered mandrel segment similar to tapered dilation mandrel 131, asshown in FIG. 8C.

Referring to FIG. 4, when coupled together, stent retaining mandrel 134and stent enclosing mandrel 138 form hourglass shaped mandrel assembly143. Hourglass shaped mandrel assembly 143 is configured such that theconical region of stent retaining mandrel 134 is oriented toward theconical region of stent enclosing mandrel 138, wherein apex end 136 ofstent retaining mandrel 134 having extending neck region 137 is incontact with apex end 141 of stent enclosing mandrel 138. Neck region137 is configured to conform to the diameter of apex end 136 of stentretaining mandrel 134 and apex end 141 of stent enclosing mandrel 138,whether or not apex end 141 and apex end 136 are equal in diameter. Neckregion 137 may vary in diameter or may be eliminated entirely.

The size and shape of hourglass shaped mandrel assembly 143 andspecifically the size of the conical regions of stent retaining mandrel134 and stent enclosing mandrel 138 preferably correspond to the sizeand shape of first flared region 102, neck region 104 and second flaredregion 106 of stent 110. Hourglass shaped mandrel assembly 143 may beasymmetrical such that diameter D4 of large diameter end 135 isdifferent than diameter D5 of large diameter end 142. Alternatively,diameter D4 and diameter D5 may be the same. Similarly, angle θ1 andangle θ2 may be different, resulting in an asymmetrical mandrel, or maybe the same. Angle θ1 and angle θ2 also may vary along the length ofhourglass shaped mandrel assembly 143 to better conform to stent 110.While neck diameter D6 may vary at different points along neck region137, diameter at neck region 137 is at all times smaller than diameterD4 and D5.

FIGS. 5-7, represents sequential views of first graft tube 122 beingloaded onto the tapered dilation mandrel 131 and being concentricallyengaged about hourglass shaped mandrel assembly 143 in an exemplarysequence. Engagement of first graft tube 122 over tapered dilationmandrel 131 may be facilitated by forming tabs on first end 153 of firstgraft tube 122 by cutting longitudinal slits (not shown) alongdiametrically opposing sides of the graft tube. The tabs may then beused to retain first graft tube 122 while axial force 150 is applied toassembly apparatus 130. Alternatively, the tabs may be used to manuallypull first graft tube 122 over tapered dilation mandrel 131 andhourglass shaped mandrel assembly 143. To prevent formation of seams orwrinkles, it is important to avoid applying torsional forces to grafttubes by twisting the graft during engagement of the graft member ontothe assembly apparatus. Cutting crevice 151 and 152 may be incorporatedinto stent retaining mandrel 134 and stent enclosing mandrel 138 toprovide a guiding indentation for a cutting element to cut first grafttube 122 and second graft tube 124.

Referring now to FIG. 5, first graft tube 122 may be engaged withtapered dilatation mandrel 131 by applying an axial force 150 toassembly apparatus 130 which causes the tapered dilatation mandrel topass into and through lumen 154 of first graft tube 122. As first grafttube 122 passes over second end 133 of tapered dilatation mandrel 131,the inner diameter of first graft first 122 is expanded radially to thatof the outer diameter of second end 133 of tapered dilation mandrel 131.As first graft tube 122 is moved axially over large diameter end 135 ofstent retaining mandrel 134 the inner diameter of first graft tube 122is greater than the outside diameter of hourglass shaped mandrelassembly 143. Axial force 150 is applied until first end 153 of firstgraft tube 122 is near large diameter end 142 of stent enclosing mandrel138. As first graft tube moves axially over second end 133 of tapereddilatation mandrel 131 and is positioned over hourglass shaped mandrelassembly 143, first graft tube 122 undergoes radial recoil so that theinner diameter of first graft tube 122 reduces until it's met withresistance from hourglass shaped mandrel 143. As illustrated in FIG. 6,first graft tube 122 has radially recoiled onto hourglass shaped mandrelassembly 143 as well as into cutting crevices 151 and 152.

FIGS. 6 and 7 illustrate the steps for separating first graft tube 122and depositing graft layer 170 upon hourglass shaped mandrel 143.Cutting blades 160 and 161 may be used to make circumferential cuts infirst graft tube 122 near the large diameter ends of stent retainingmandrel 134 and stent enclosing mandrel 138. For example, cutting bladesmay make circumferential cuts at the position of cutting crevices 151and 152. Cutting crevices 151 and 152 are positioned at a length longerthan the length of stent 110 to account for recoil of graft materialafter being cut. Alternatively, where the stent is only partiallyencapsulated, cutting crevices 151 and 152 may be positioned at a lengthshorter than the length of stent 110. After cutting first graft tube 122with cutting blades 160 and 161, first graft layer 170 is deposited ontostent 110. Alternatively, only cutting crevice 151 and cutting blade 160may be used to create a circumferential cut near the large diameter endof stent retaining mandrel 134. In this manner first end 153 of firstgraft tube 122 having tabs at the end, may serve as one end of firstgraft layer 170. First graft layer 170 has a length longer than stent110. As such, a section of first graft layer 170 extends beyond opposingends of stent 110. After removing excess grafting material, first graftlayer 170 remains on the assembly apparatus and covers hourglass shapedmandrel assembly 143. Tape may be applied to first graft layer 170 tosecure graft layer 170 to stent retaining mandrel 134. Upon depositingfirst graft layer 170 on hourglass shaped mandrel assembly 143, anoptional step involves applying a layer of Fluorinated EthylenePropylene (FEP), or any other adhesive material, to first graft layer170 for improving adhesion during encapsulation process.

Referring now to FIGS. 8A-8C, after depositing first graft layer 170 onhourglass shaped mandrel assembly 143, stent 110 may be loaded ontohourglass shaped mandrel assembly 143. One method for loading stent 110onto hourglass shaped mandrel assembly 143 is to uncouple stentretaining mandrel 134 and stent enclosing mandrel 138. When stentretaining mandrel 134 is uncoupled from stent enclosing mandrel 138, theportion of first graft layer 170 in contact with stent retaining mandrel134 and neck region 137 will remain supported by the stent retainingmandrel 134 but the portion that was in contact with stent enclosingmandrel 138 will become unsupported beyond neck region 137. As shown inFIG. 8A, by uncoupling stent retaining mandrel 134 and stent enclosingmandrel 138, stent 110 may be loaded onto stent retaining mandrel 134over first graft layer. During this step, the unsupported region offirst graft layer 170 may be manipulated in shape and guided through aninterior opening of neck region 104 and through an interior of secondflared region 106. Where first end 153 of first graft tube 122 is usedas the end of first graft layer 170, the tabs on first end 153 of firstgraft tube 122 described above, may be used to help guide first graftlayer 170 through stent 110.

Stent 110 is engaged about the stent retaining mandrel 134 byconcentrically positioning the stent 110 over first graft layer 170 andstent retaining mandrel 134. When loaded onto stent retaining mandrel134, first flared region 102, and neck region 104 of stent 110 engagewith stent retaining mandrel 134 while second flared region 106 doesnot. Stent retaining mandrel 134 and first graft layer 170 areconfigured to have a combined diameter which is less than the innerdiameters of first flared region 102 and neck region 104 of stent 110,allowing stent to slide onto stent retaining mandrel 134.

Referring now to FIG. 8B, upon loading stent 110 on stent retainingmandrel 134 and first graft layer 170, stent enclosing mandrel 138 iscoupled to stent retaining mandrel 134, completing the hourglass shapedmandrel assembly. First graft layer 170 may be manually manipulated toavoid being damaged and prevent the occurrence of any wrinkles duringrecoupling of stent enclosing mandrel 138. For example, first graftlayer 170 may be held by the tabs described above while the stentenclosing mandrel is recoupled to the stent retaining mandrel. If firstgraft layer was taped to stent retaining mandrel 134, the tape may beremoved after recoupling. When stent enclosing mandrel 138 is coupled tostent retaining mandrel 134, stent enclosing mandrel 138 engages bothfirst graft layer 170 and second flared region 106 of stent 110, lockingstent 110 into position between large diameter end 135 and largediameter end 142. Stent enclosing mandrel 138 and first graft layer 170are configured to have a combined outside diameter which is less thanthe inner diameter of second flared region 106 of stent 110, allowingstent 110 to slide into position on stent enclosing mandrel 138. Uponplacing stent 110 on first graft layer 170, an optional step involvesapplying a layer of FEP, or any other adhesive material, to first graftlayer 170 and stent 110 for improving adhesion during encapsulationprocess.

While FIGS. 5-7 illustrate one sequence for generating first graft layer170, it is appreciated that first graft layer 170 may be deposited ontoassembly apparatus 130 in different ways. For example, first graft layer170 may not be separated from first graft tube 122 until after stent 110has been loaded onto assembly apparatus 130. In this approach, afterfirst end 153 of first graft tube 122 is positioned near large diameterend 142 of stent enclosing mandrel 138 and first graft tube 122undergoes radial recoil so that the inner diameter of first graft tube122 reduces until it is met with resistance from hourglass shapedmandrel 143, as shown in FIG. 6, stent retaining mandrel 134 may beuncoupled from stent enclosing mandrel 138. Like in the sequencedescribed above, the portion of the first graft tube extending beyondneck region 137 will become unsupported after stent enclosing mandrel138 has been uncoupled. The unsupported region of first graft tube 122may then be manipulated in shape and guided through an interior openingof neck region 104 and through an interior of second flared region 106as described above. After the stent enclosing mandrel has been recoupledas shown in FIGS. 8A-8B and discussed above, cuts may be made usingcutting blades 160 and 161 to separate first graft tube 122 from firstgraft layer 170.

In yet another example, first graft layer 170 may be deposited ontohourglass shaped mandrel assembly 143 using an electrospinning process.Electrospinning is a process in which polymers are electrospun intoultrafine fibers which are deposited upon a target surface. Theelectrospinning process involves applying an electric force to drawfibers out of polymer solutions or polymer melts. Using electrospinning,ultrafine fibers, such as ePTFE fibers may be deposited onto hourglassshaped mandrel assembly 143 to form first graft layer 170. Assemblyapparatus may be continuously rotated about its longitudinal axis toevenly apply the ePTFE fibers. In one example, stent retaining mandrel134 and stent enclosing mandrel 138 may be coupled together during theelectrospinning process. In another example, stent retaining mandrel 134and stent enclosing mandrel 138 may be uncoupled and the conical regionof stent retaining mandrel 134 including neck region 137 may besubjected to the electrospinning process separate from the conicalregion of stent enclosing mandrel 138. Subsequently, when stentenclosing mandrel 138 and stent retaining mandrel 134 are coupledtogether, the ePTFE fibers on stent retaining mandrel 134 may besintered together to form a continuous first graft layer 170. Secondgraft layer 190 may similarly be deposited using electrospinning.

Referring now to FIG. 8C, assembly apparatus 130 may be configured suchthat first graft tube 122 and second graft tube 124 may be loaded ontoassembly apparatus 130 from the side closest to stent enclosing mandrel138. As discussed above, stent enclosing mandrel 138 may be removablycoupled to handle segment 144. In the alternative configuration shown inFIG. 8C, stent enclosing mandrel 138 may be uncoupled from handlesegment 144 and tapered dilation mandrel 131′ may be coupled to stentenclosing mandrel 138 instead. It will be understood by those in the artthat the couplings are interchangeable and may be any of a wide varietyof suitable couplings. Tapered dilation mandrel 131′ has first end 132′and second end 133′ wherein the diameter of second end 133′ is greaterthan the diameter of first end 132′ and the diameter of second end 133′is equal to the diameter of large diameter end 142 of stent enclosingmandrel 138. In the configuration shown in FIG. 8C, large diameter end135 may also perform as handle segment 144′ for pushing.

Using the configuration shown in FIG. 8C, an axial force 165 may beapplied to assembly apparatus 130 to cause tapered dilatation mandrel131′ having first end 132′ to pass into and through the lumen of thefirst graft tube 122. Similarly, axial force 165 may be applied toassembly apparatus 130 to guide assembly apparatus 130, and specificallyfirst end 132′, into stent 110 which is configured to expand as tapereddilatation mandrel 131′ is pushed into stent 110. Axial force 165 may beapplied by using handle segment 144′ to push assembly apparatus 130. Byengaging first end 132′ with expandable stent 110 exhibiting springtension, stent 110 may be dilated as it moves along tapered dilatationmandrel 131′. In this manner, first end region diameter D1, second endregion diameter D2, and neck diameter D3 of stent 110, as shown in FIG.1, may be expanded to a diameter equal to or larger than large diameterend 142 of stent enclosing mandrel 138, thus permitting stent 110 totraverse large diameter end 142. As stent 110 exhibiting spring tensionis passed over hourglass shaped mandrel assembly 143, it encounters noresistance to radial recoil and thus radially recoils into position overfirst graft layer 170 and between large diameter end 135 and largediameter end 142. Alternatively, stent 110 may be expanded to a slightlylarger diameter than second diameter end 142 by applying a radiallyexpansive force on stent 110 using an external expansion tool. In thisexample, after expanding stent 110 to the appropriate diameter, stent110 may be concentrically placed over stent enclosing mandrel 138 andallowed to radially recoil into position over hourglass shaped mandrelassembly 143 having first graft layer 170 deposited on an outer surface.

In yet another alternative arrangement, stent enclosing mandrel 138 mayalternatively be comprised of a cylindrical region instead of a conicalregion. The cylindrical region may have the same diameter as neck region137 such that the cylindrical region of stent enclosing mandrel 138 mayappear as an extension of neck region 137 when stent enclosing mandrel138 is coupled to stent retaining mandrel 134. In this alternativeembodiment, stent enclosing mandrel 138 also may be coupled to tapereddilation mandrel 131′ which may have second end 133′ that is equal indiameter to neck region 137 and smaller in diameter than first end 132′.Stent enclosing mandrel 138 having the cylindrical region instead of aconical region, may be used to encapsulate a stent having a conicalregion and a neck region that forms a conduit. Any of the methods andtechniques described herein to encapsulate the hourglass shaped stentmay be used to encapsulate the stent having the cylindrical regioninstead of the conical region. Upon completion of encapsulation, theencapsulated stent may be gently removed from assembly apparatus 130 bysliding the encapsulated stent over the tapered dilation mandrel 131′.Alternatively, stent enclosing mandrel 138 may be uncoupled from stentretaining mandrel 134.

FIGS. 9-11 represent sequential views of the second graft tube 124 beingloaded onto the tapered dilation mandrel 131 and being concentricallyengaged about stent 110. Engagement of second graft tube 124 overtapered dilation mandrel may be facilitated by forming tabs on first end171 of second graft tube 124 similar to the method described above,involving cutting longitudinal slits (not shown) along diametricallyopposed sides of the graft member. The tabs may then be used to retainthe second graft tube 124 while axial force 175 is applied to assemblyapparatus 130. Alternatively, the tabs may be used to manually pullsecond graft tube 124 over tapered dilation mandrel 131 and hourglassshaped mandrel assembly 143.

Referring now to FIG. 9, second graft tube 124 may be engaged withtapered dilation mandrel 131 in much the same way as first graft tube122—by applying axial force 175 to assembly apparatus 130 which causesthe tapered dilation mandrel to pass into and through lumen 173 ofsecond graft tube 124. As second graft tube 124 passes over second end133 of tapered dilation mandrel 131, the inner diameter of second grafttube 124 is radially expanded to that of the outer diameter of secondend 133 of tapered dilation mandrel 131. The assembly apparatus 130 ispassed into and through lumen 173 of second graft tube 124 until firstend 171 of second graft tube 124 is close to large diameter end 142 ofstent enclosing mandrel 138. As second graft tube moves axially overstent 110 and to a position over large diameter end 142 of stentenclosing mandrel 138, second graft tube 124 undergoes radial recoil sothat the inner diameter of second graft tube 124 reduces until it is metwith resistance. As illustrated in FIG. 10, second graft tube 124 isradially recoiled onto stent 110. Second graft tube 124 also may beradially recoiled into cutting crevices 151 and 152.

Alternatively, second graft tube 124 may be positioned onto stent 110via an assembly apparatus 130 that is configured to expand and/orcontract radially. Assembly apparatus may be comprised of materialhaving expansion properties or contraction properties which may beresponsive to exterior conditions. For example, hourglass shaped mandrelassembly 143 may be compressible by applying a force normal to thesurface of hourglass shaped mandrel 143. Instead, assembly apparatus 130may be comprised of material having a high coefficient of thermalexpansion permitting the hourglass shaped assembly to contract whenplaced in a low temperature environment and expand when placed in a hightemperature. Alternatively, assembly apparatus may have a rigid core andmultiple surfaces that move independently from one another, the surfacesbeing connected to the core by a number of springs that are configuredto permit movement of the surfaces relative to the core when a normalforce is applied to the surfaces. For example, a surface may compresstowards the core when a normal force is applied and the same surface mayexpand radially out from the rigid core when the normal force isreleased. In addition, or alternatively, the core of the assemblyapparatus 130 may have a screw assembly embedded within the core andconfigured to translate a rotational force applied to the screw assemblyinto a radial force which is applied to the surfaces to push thesurfaces radially outward, or pull the surfaces radially inward.

Expandable stent 110 having spring tension may be positioned oncompressible hourglass shaped mandrel assembly 143 and stent andassembly together may be compressed when a compressive radial force isapplied. At a certain compressive force, first end region diameter D1and second end region diameter D2 of stent 110 may be compressed to neckdiameter D3. In this compressed state, second graft tube 124 may beeasily moved axially over compressed stent 110 and first graft layer170. Subsequent to positioning second graft tube 124 over compressedstent 110 and first graft layer 170, compressive force applied to stent110 and compressible hourglass shaped mandrel assembly 143 may bereleased. At the same time, hourglass shaped mandrel assembly 143 may beexpanded. In this way second graft tube 124 may be engaged with stent110.

FIGS. 10 and 11 illustrate the steps for separating second graft tube124 from stent-graft assembly 120. After depositing second graft tube124 on stent 110, cutting blades 160 and 161 may again be used to makecircumferential cuts in second graft tube 124 at a position near thelarge diameter ends of stent retaining mandrel 134 and stent enclosingmandrel 138. For example, cutting blades 160 and 161 may makecircumferential cuts at the position of cutting crevices 151 and 152. Asexplained above, cutting crevices 151 and 152 may be positioned at alength longer than the length of stent 110 to account for recoil ofgraft material upon being cut. After cutting second graft tube 124 withcutting blades 160 and 161, second graft layer 190 is deposited ontostent 110 which is positioned over graft layer 170. Second graft layer190 has a length longer than stent 110. As such, a section of secondgraft tube 124 extends beyond opposing ends of stent 110 and is similarin length to first graft layer 170. Waste portion of second graft tube124 remaining on assembly apparatus 130 may be discarded. Where stent110 is only partially encapsulated, first graft layer 170 and/or secondgraft layer 190 may have a length shorter than stent 110 and thus maynot extend beyond opposing ends of stent 110. For example, only firstflared region 102 or second flared region 106 may be encapsulated. Wherestent 110 takes a different asymmetric shape, such as an hourglass shapeon one side and a straight tube shape on the other side, only oneportion of asymmetric stent 110 may be encapsulated.

To securely bond first graft layer 170 to second graft layer 190,pressure and heat may be applied the stent-graft assembly to achievesintering. Sintering results in strong, smooth, substantially continuouscoating that covers the inner and outer surfaces of the stent. Sinteringmay be achieved by first wrapping the ends of first graft layer 170 andsecond graft layer 190 with strips of tape such as TFE or ePTFE tape tosecure the stent-graft assembly to the mandrel. To apply pressure,stent-graft assembly 120 attached to assembly apparatus 130 may beplaced in a helical winding wrapping machine which tension wraps thestent-graft assembly 120 with at least one overlapping layer of tape.For example, stent-graft assembly 120 may be wrapped with a singleoverlapping layer of ½ inch ePTFE tape with an overlap of the winding ofabout 70%. The force exerted by the TFE or ePTFE wrapping tapecompresses the stent-graft assembly against the hourglass shaped mandrelassembly 143, thereby causing the graft layers to come into intimatecontact through interstices of stent 110. In stent 110 shown in FIG. 1.,interstices exist in the between the struts and sinusoidal rings.Varying tape thickness may reduce or improve ePTFE conformance. Forexample, thicker tape may result in more compression uniformity thanthinner tape material.

Stent-graft assembly 120 attached to assembly apparatus 130 may then beheated by placing the stent-graft assembly and assembly apparatus into aradiant heat furnace. For example, stent-graft assembly 120 may beplaced into a radiant heat furnace which had been preheated. In oneexample, sintering may be achieved at 327° C. The humidity within theradiant heat furnace may preferably be kept low. The stent-graftassembly may remain in the radiant heat furnace for a time sufficientfor first graft layer 170 to sinter to second graft layer 190. In oneexample, stent-graft assembly 120 may remain in the furnace for about7-10 minutes. The heated assembly may then be allowed to cool for aperiod of time sufficient to permit manual handling of the assembly.After cooling, the helical wrap may be unwound from stent-graft assembly120 and discarded. The encapsulated stent may then be concentricallyrotated about the axis of the mandrel to release any adhesion betweenthe first graft layer 170 and hourglass shaped mandrel assembly 143. Theencapsulated stent, still on the mandrel, may then be placed into alaser trimming fixture to trim excess graft materials away fromstent-graft assembly 120. In addition, the encapsulated stent may betrimmed at various locations along the stent such as in the middle ofthe stent, thereby creating a partially encapsulated stent.

Alternatively, first graft layer 170 may be sintered to second graftlayer 190 by inducing pressure. For example, assembly apparatus 130 orat least hourglass shaped mandrel assembly 143 may have smallperforations which may be in fluid communication with a vacuum pumpsituated in an inner lumen of assembly apparatus 130 or otherwise influid communication with an inner lumen of assembly apparatus 130.Additionally or alternatively, the assembly apparatus 130 may be placedin a pressurized environment that is pressurized using a compressorpump, for example. In another example, a balloon such as a Kevlarballoon may also or alternatively be applied to the exterior of thestent-graft assembly to apply pressure to the stent-graft assembly. Viathe pressure applied, the first graft layer 170 may collapse on thesecond graft layer 190 forming even adhesion. A combination of bothpressure and heat may also be used to sinter the first graft layer 170to the second graft layer 190. Trimming may then take place in the samemanner as described above.

After trimming excess graft materials, stent-graft assembly 120 may beremoved by decoupling stent retaining mandrel 134 from stent enclosingmandrel 138. Upon decoupling stent retaining mandrel 134 and stentenclosing mandrel 138, stent-graft assembly 120 remains supported bystent retaining mandrel 134. Stent-graft assembly 120 may then beremoved from stent retaining mandrel 134 by axially displacingstent-graft assembly 120 relative to stent retaining mandrel 134.

Upon removal of stent-graft assembly 120 from assembly apparatus 130,stent-graft assembly 120 may be manipulated to a reduced first endregion diameter D1, second end region diameter D2 and neck regiondiameter D3. The assembly stent-graft assembly may achieve these smallerdiametric dimensions by methods such as crimping, calendering, folding,compressing or the like. Stent-graft assembly 120 may be constrained atthis dimension by disposing stent-graft assembly 120 in a similarlysized cylindrical sheath. Once positioned in the sheath, stent-graftassembly 120 may be delivered to an implantation site using a catheterbased system including a delivery catheter. The catheter based systemmay further comprise an engagement component for temporarily affixingstent-graft assembly 120 to the delivery catheter. U.S. Pat. No.9,713,696 to Yacoby, incorporated herein by reference, describes anexemplary engagement component. The engagement component may beconfigured to disengage the stent-graft assembly 120 from the deliverycatheter when stent-graft assembly 120 has reached the delivery site. Atthe delivery site, the sheath may be removed to release the constrainingforce and permit the intraluminal stent to elastically expand in theappropriate position.

While the approach set forth above describes depositing a layer ofbiocompatible material on an interior surface of stent 110 and anexterior surface of stent 110, it is understood that the stent 110 maybe coated with only one layer of biocompatible material. For example,stent 110 may be engaged with only first graft layer 170 along aninterior surface, following only the appropriate steps set forth above.Alternatively, stent 110 may be engaged with only second graft layer 190along an exterior surface, following only the appropriate steps setforth above.

As explained above, stent 110 may be comprised of a plurality ofsinusoidal rings connected by longitudinally extending struts. However,it is understood that stent 110 may be constructed from a plurality ofinterconnected nodes and struts having varying distances and formingvarious shapes and patterns. In one embodiment the inter-nodal-distance(IND) of stent 110 may be manipulated by controlling the tension of thebiocompatible material layers during encapsulation. For example, thestent may be encapsulated in a manner providing different pulling forceson stent 110. This may enable different functionality of various areasof the encapsulated stent which are known to be influenced by IND. Inone example, by controlling tension of the biocompatible material layersduring encapsulation, different functionality of various areas withrespect to tissue ingrowth characteristics may be achieved. Further, itis understood that encapsulation may be performed such that stent 110 isconstrained in a restricted or contracted state by the encapsulationmaterial. For example, the neck diameter may be decreased from 6 mm to 5mm. This may permit controlled in-vivo expansion to a fully expandedstate using, for example, balloon inflation, whereby the constraint isremoved. This procedure may be beneficial in a case where a clinicalcondition dictates an initial restricted state for delivery but requiresa larger unconstrained state for implantation or treatment.

Referring now to FIGS. 12A-D, an alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated.FIGS. 12A-D represent sequential views of first graft tube 122 andsecond graft tube 124 being loaded onto and concentrically engaged aboutstent-graft assembly 120. As shown in FIG. 12A the process may start byengaging first graft tube 122 over stent 110. Stent 110 may be crimpedto a diameter smaller than first graft tube 122 and guided into grafttube 122. Alternatively, or in addition to, first graft tube 122 may bestretched to a diameter slightly larger than stent 110 using anexpanding mandrel or other stretching technique and guided over stent110.

Upon positioning first graft tube 122 over stent 110, second graft tube124 may be positioned within and along the entire length of stent 110,shown in FIG. 12B. Second graft tube 124 may be pulled through stent 110while stent 110 remains engaged with first graft tube 122. Subsequently,as shown in FIG. 12C, female mandrel 195 may be introduced near secondflared region 106 of stent 110. Female mandrel 195 may have a similarshape as second flared region 106 only with slightly smaller dimensions.Female mandrel 195 may have receiving portion 196 designed to receivemale mandrel 197. Having a conical shape, female mandrel 195 may begently advanced within second graft tube 124 until female mandrel 195takes up nearly the entire space within second flared region 106. Inthis manner, second graft tube 124 may be engaged with stent 110 alongan interior surface of second flared region 106 and, in someembodiments, neck region 104.

Referring now to FIG. 12D, male mandrel 197 may be introduced near firstflared region 102. Male mandrel 197 may be similar in shape to firstflared region 102 only with slightly smaller dimensions. Male mandrel197 may have protruding section 198 sized and shaped to be received byfemale mandrel 195. Having a conical shape, male mandrel 197 may begently advanced within second graft tube 124 toward female mandrel 195until female mandrel 195 takes up nearly the entire space within firstflared region 102 and protruding section is fully received by receivingportion 196. In this manner, second graft tube 124 may be engaged withstent 110 along an interior surface of second flared region 106 and, insome embodiments, neck region 104.

Upon engaging female mandrel 195 and male mandrel 197, stent 110 may beentirely covered on an exterior surface by first graft tube 122 andentirely covered on an interior surface by second graft tube 124. Firstgraft tube 122 and second graft tube 124 may be appropriately cut awayaccording to the same procedures illustrated in FIGS. 6 and 10 resultingin first graft layer 170 and second graft layer 190. Further,stent-graft assembly 120 may be produced using the same proceduresdetailed above including the procedures for securely bonding first graftlayer 170 to second graft layer 190 involving pressure and heat appliedto the stent-graft assembly to achieve sintering. It is understood thatthe mandrel placed in the first flared region 102 may alternatively be afemale mandrel and the mandrel placed in second flared region 106 mayalternatively be a male mandrel. It is also understood that the processdepicted in FIGS. 12A-D may start first with the mandrel entering thefirst flared region 102 of stent 110.

Referring now to FIGS. 13A-13E, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 13A, first graft layer 170 may be pre-formed into anhourglass shaped pre-formed first graft layer 199 using a dedicatedmandrel and heat treatment. The pre-formed shape may have dimensionssimilar to that of stent 110. Heat may be applied to pre-formed firstgraft layer 199 to maintain its shape. Upon forming pre-formed firstgraft layer 199, female mandrel 200 may be introduced into one side ofpre-formed first graft layer 199, such that female mandrel 200 takes upnearly the entire space within one hourglass side of pre-formed firstgraft layer 199 as shown in FIG. 13B. Female mandrel 200 may havereceiving portion 201 designed to receive male mandrel 203.

Upon placing female mandrel 200 within pre-formed first graft layer 199,stent 110 may be placed over pre-formed first graft layer 199, as showin in FIG. 13C. Stent 110 may be positioned over pre-formed first graftlayer 199 or pre-formed first graft layer 199 may be positioned withinstent 110. Stent 110, having a shape similar to that of pre-formed firstgraft layer 199 should fit into place on pre-formed first graft layer199.

Once stent 110 is deposited on pre-formed first graft layer 199,pre-formed second graft layer 202, formed into an hourglass shape havingdimensions similar to stent 110 may be deposited on stent 110 as isillustrated in FIG. 13D. Pre-formed second graft layer 202 may be formedin a similar manner as pre-formed first graft layer 199, using adedicated mandrel and heat treatment. Pre-formed second graft layer 202may be expanded and positioned over stent 110. Pre-formed second graftlayer 202, may recoil into its pre-shaped form upon releasing any radialexpansion force on pre-formed second graft layer 202. Alternatively, orin addition to, stent 110 may be crimped to facilitate mounting ofpre-formed second graft layer 202.

Referring now to FIG. 13E, male mandrel 203 may be introduced near theend of pre-formed first graft layer 199 not occupied by female mandrel200. Male mandrel 203 may be similar in shape to this end of pre-formedfirst graft layer 199 only with smaller dimensions. Male mandrel 203 mayhave protruding section 204 sized and shaped to be received by receivingportion 201 of female mandrel 200. Having a conical shape, male mandrel203 may be gently advanced within pre-formed first graft layer 199toward female mandrel 200 until protruding section 204 is fully receivedby receiving portion 201.

Upon engaging female mandrel 200 and male mandrel 203, stent 110 may beat least partially covered on an exterior surface by pre-formed secondgraft layer 202 and at least partially covered on an interior surface bypre-formed first graft layer 199. Stent-graft assembly 120 may beproduced using the same procedures detailed above including theprocedures for securely bonding first graft layer 170, in this casepre-formed first graft layer 199, to second graft layer 190, in thiscase pre-formed second graft layer 202. These procedures may involvepressure and heat applied to the stent-graft assembly to achievesintering. This process simplifies the mounting of the graft tubes andreduces risk of tears and non-uniformities. It is understood that themandrel inserted first into pre-formed first graft layer 199 mayalternatively be a male mandrel and the mandrel inserted second mayalternatively be a female mandrel.

Referring now to FIGS. 14A-14D, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 14A, the process may start by engaging first graft tube122 over stent 110. Stent 110 may be crimped using dedicated crimpingtools, such as ones detailed in U.S. Pat. No. 9,713,696 to Yacoby, theentire contents of which are incorporated herein by reference, to adiameter smaller than first graft tube 122 and guided into graft tube122. Alternatively, or in addition to, first graft tube 122 may bestretched to a diameter slightly larger than stent 110 using anexpanding mandrel or other stretching mechanism and guided over stent110. The approach illustrated in FIG. 14A may achieve a firm engagementbetween crimped stent 110 and the first graft layer 170, enablingimproved encapsulation.

Upon positioning first graft tube 122 over stent 110, second graft tube124 may be positioned within and along the entire length of stent 110,shown in FIG. 14B. Second graft tube 124 may be pulled through stent 110while stent 110 remains engaged with first graft tube 122.Alternatively, stent 110, with first graft tube 122 engaged with stent110 may be expanded, using well-known expansion techniques, andpositioned over second graft tube 124. Subsequently, as shown in FIG.14C, balloon catheter 205 having inflatable balloon 206 may be insertedinto second graft tube 124 such that the balloon catheter 205 issurrounded by stent 110 and first graft tube 122. Alternatively, secondgraft tube 124 may be positioned over inflatable balloon 206 andinflatable balloon 206 may be positioned within stent 110 via ballooncatheter 205.

Referring now to FIG. 14D, upon positioning balloon catheter 205 intosecond graft tube 124, inflatable balloon 206 of balloon catheter 205may be inflated to engage second graft tube 124 with an interior surfaceof stent 110. Using inflatable balloon 206 to engage second graft tube124 with stent 110 permits uniform contact between and engagementbetween second graft tube 124 and stent 110 as well as second graft tube124 and first graft tube 122 between the interstices of stent 110, thusoptimizing the adhesion during encapsulation. The degree of inflationmay be manipulated to achieve a desired pressure within the balloon anda desired adhesion between first graft tube 122 and the second grafttube 124. Additionally, the degree of inflation may be manipulated toachieve a desired inter-nodal-distance of the graft material. Differentpressures may also be achieved by varying the wall thickness of theballoon. Furthermore, interlocking balloons may be used to reduce bondlines.

First graft tube 122 and second graft tube 124 may be appropriately cutaway according to the same procedures illustrated in FIGS. 6 and 10resulting first graft layer 170 and second graft layer 190. Further,stent-graft assembly 120 may be produced using the same proceduresdetailed above including the procedures for securely bonding first graftlayer 170 to second graft layer 190 involving pressure and heat appliedto the stent-graft assembly to achieve sintering.

Referring now to FIGS. 15A-15F, another alternative method of makingstent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. Asshown in FIG. 15A, the process may start by placing stent 110 withinfunnel 207 and advancing stent 110 within funnel 207 towards a reducedsection of funnel 207, using, for example, a dedicated pusher tool likethe one described in U.S. Pat. No. 9,713,696 to Yacoby, to reduce thediameter of stent 110. Stent 110 may be constructed in a manner that,upon reduction caused by funnel 207, the shape of stent 110 morphs suchthat the flared ends are tapered and eventually turned inward toward alongitudinal axis of stent 110, resulting in stent 110 having asubstantially reduced cross-sectional diameter.

As is shown in FIG. 15B, funnel 207 may have introducer tube 208extending from the narrow side of the funnel 207 which may receive stent110 after stent 110 has been fully restricted by funnel 207. It isunderstood that tube 208 and funnel 207 may be the same component or maybe different components that are coupled together (e.g., screwedtogether). Introducer tube 208 may have a diameter smaller than that offirst graft tube 122. Introducer tube may thus be inserted into firstgraft tube 122, as is illustrated in FIG. 15C, and stent 110 having thereduced diameter, may be advanced out of introducer tube 208 and intofirst graft tube 122. Alternatively, it is understood that introducertube 208 may have a diameter the same size as or larger than that ofgraft tube 122 and graft tube 122 may be stretched and mounted overintroducer tube 208.

Referring now to FIG. 15D, stent 110 is illustrated after having beenadvanced from introducer tube 208 and into first graft tube 122. As isshown in FIG. 15D, upon the removal of inward radial force fromintroducer tube 208, stent 110 may expand radially to a diameter largerthan the diameter of first graft tube 122, thereby engaging first grafttube 122 along the outer surface of stent 110. An end of first grafttube 122 may have been positioned a distance beyond introducer tube 208such that upon depositing stent 110 into first graft tube 122, remainingportion 209 of first graft tube 122 extends beyond stent 110 a distanceof more than one length of stent 110.

Referring now to FIG. 15E, remaining portion of first graft tube 122 maybe used as a second graft layer along the internal surface of stent 110by pushing remaining portion 209 through the interior of stent 110 andout an opposing side of stent 110, in the direction indicated by thearrows in FIG. 15D. In this manner, first graft to 122 may extend alongan exterior surface of stent 110, curve around an end of stent 110 andtravel along the interior of stent 110.

To engage remaining portion 209 with the interior surface of stent 110,female mandrel 200 having receiving portion 201 and male mandrel 203having protruding section 204 may be inserted into the stent-graftcombination. Female mandrel 200 may be introduced first to one end ofthe stent-graft combination having a size slightly larger than thedimensions of female mandrel 200. Subsequently, male mandrel 203 may beintroduced into the opposing end of the stent-graft combination andadvanced until protruding section 204 is received by receiving portion201. As female mandrel 200 and male mandrel 203 are inserted, stent 110may be guided into its original hour-glass shape. This method may induceimproved adhesion between first graft tube 122, remaining portion 209and stent 110.

Upon engaging female mandrel 200 and male mandrel 203, first graft tube122 and remaining portion 209 may be appropriately cut away according tothe same procedures illustrated in FIGS. 6 and 10 resulting first graftlayer 170 and second graft layer 190, with the exception that only oneside of stent-graft assembly 120 needs to be cut or otherwise removedfirst graft tube 122 and remaining portion 209. Stent-graft assembly 120may be produced using the same procedures detailed above including theprocedures for securely bonding first graft layer 170 to second graftlayer 190 involving pressure and heat applied to the stent-graftassembly to achieve sintering. It is also understood that the processdepicted in FIG. 15F may start with the male mandrel entering thestent-graft combination first.

Referring now to FIGS. 16A-D, stent 110 may alternatively be coveredwith a single tube of biocompatible material, as shown in FIG. 16A, tocreate stent-graft assembly 210 having varying layers of biocompatiblematerial (e.g., two-to-three layers of biocompatible material). Grafttube 216, which is a tube of biocompatible material, has first graftportion 211, second graft portion 212, and third graft portion 213.Graft tube 216 has a length that is longer that the length of stent 110and preferably greater than twice the length of stent 110. First graftportion 211 begins at first end 214 of graft tube 216 and extends tosecond graft portion 212. Second graft portion 212 extends between firstgraft portion 211 and third graft portion 213 and is continuously joinedto first graft portion 211 and third graft portion 213. Third graftportion 213 ends at second end 215 of graft tube 216. FIGS. 17A-22Billustrate an exemplary approach for depositing graft tube 216 on stent110 in the configuration shown in FIGS. 16A-D.

The cross sections of stent-graft assembly 210 illustrated in FIG. 16A(cross-sections B, C, and D) are illustrated in FIGS. 16B, 16C, and 16D,respectively. Referring now to FIG. 16B, cross-section B of stent-graftassembly 210 is illustrated. As is shown in FIG. 16B, first flaredregion 102 of stent 110 is covered on the inside and outside by grafttube 216. Specifically, first flared region 102 is covered on theoutside by third graft portion 213 and on the inside (i.e., on theinterior of first flared region 102) by second graft portion 212.Accordingly, stent 110 is covered at first flared region 102 by twolayers of biocompatible material.

Referring now to FIG. 16C, cross-section C of stent-graft assembly 210is illustrated. As is shown in FIG. 16C, neck region 104 of stent 110 iscovered by two layers of biocompatible material on the outside and onelayer of biocompatible material on the inside. Specifically, stent 110is first covered on outside by first graft portion 211, which is coveredby third graft portion 213. On the inside (i.e., on the interior of neckregion 104), stent 110 is covered by second graft portion 212.Accordingly, stent 110 of stent-graft assembly 210 is covered at neckregion 104 by three layers of biocompatible material.

Referring now to FIG. 16D, cross-section D of stent-graft assembly 210is illustrated. As is shown in FIG. 16D, second flared region 106 ofstent 110 is covered on outside and inside by graft tube 216.Specifically, first flared region 102 is covered on the outside by firstgraft portion 211 and on the inside (i.e., on the interior of secondflared region 106) by second graft portion 212. Accordingly, stent 110of stent-graft assembly 210 is covered at second flared region 106 bytwo layers of biocompatible material.

As also discussed below, the layers of biocompatible material may besecurely bonded together to form a monolithic layer of biocompatiblematerial. For example, first graft portion 211, second graft portion212, and third graft portion 213 may be sintered together to form astrong, smooth, substantially continuous coating that covers the innerand outer surfaces of the stent. Portions of the coating may then beremoved as desired from selected portions of the stent usinglaser-cutting or mechanical cutting, for example.

FIGS. 17A-22D generally illustrate an exemplary method of makingstent-graft assembly 210, as depicted in FIGS. 16A-D. Referring now toFIG. 17A, to deposit the first graft portion upon the neck region andthe second flared region, the process may start by crimping stent 110.For example, stent 110 may be placed within funnel 207 and advancedwithin funnel 207 towards a reduced section of funnel 207. The reducedsection preferably is the diameter of the neck region of the stent orslightly larger. However, it is understood that stent 110 may be reducedto different diameters. As explained above with reference to FIG. 15A,stent 110 may be advanced by a dedicated pusher tool like the onedescribed in U.S. Pat. No. 9,713,696 to Yacoby. As also explained above,stent 110 may be constructed in a manner that, upon reduction caused byfunnel 207, the shape of stent 110 morphs such that the flared ends aretapered and eventually turned inward toward a longitudinal axis of stent110, resulting in stent 110 having a substantially reducedcross-sectional diameter. It is understood that stent 110 mayalternatively be compressed into a compressed state using any well-knowncompressing or crimping techniques.

As is shown in FIGS. 17B and 17C, funnel 207 may have or may be coupledto introducer tube 208 extending from the narrow side of the funnel 207which may receive stent 110 after stent 110 has been fully restricted byfunnel 207. Introducer tube 208 may have a diameter smaller than that ofthe graft tube. Alternatively, the first end of the graft tube may beexpanded to a diameter larger than that of introducer tube 208 usingwell-known expansion techniques (e.g., applying heat to the graft tube).Introducer tube 208 may thus be inserted into first end 214 of grafttube 216, as is illustrated in FIG. 17C, and stent 110 having thereduced diameter, may be partially advanced out of introducer tube 208and into graft tube 216, such that second flared region 106 and neckregion 104 are advanced into graft tube 216.

Referring now to FIG. 17D, second flared region 106 and neck region 104of stent 110 are illustrated after having been advanced from introducertube 208 and into graft tube 216 thereby releasing compressive force onsecond flared region 106 and neck region 104, if any. Upon the removalof inward radial force from introducer tube 208, at least second flaredregion 106 of stent 110 may expand radially to a diameter larger thanthe diameter of graft tube 116, thereby engaging graft tube 116 alongthe outer surface of second flared region 106 and neck region 104 in amanner that causes graft tube 216 to expand in an unstressed andunwrinkled fashion. To increase the elasticity of graft tube 216 topermit stent 110 to expand to its expanded state, heat may be applied toboth graft tube 216 and stent 110. For example, heated air may bedirected at graft tube 216 and stent 110. In an alternative approach,stent 110 may be cooled below its martensite-to-austenite transformationtemperature, such that it becomes martensite. Graft tube 116 may beloaded onto second flared region 106 and neck region 104 in thiscontracted state and permitted to slowly expand as stent 110 warms toroom temperature or an elevated temperature in a manner that causesgraft tube 216 to expand in an unstressed and unwrinkled fashion.

Referring now to FIG. 17E, after depositing first graft portion 211 ofgraft tube 216 upon second flared region 106 and neck region 104, stent110 may be completely ejected from introducer tube 208, therebyreleasing any compressive force on first flared region 102. Upon beingejected from introducer tube 208, stent 110 may return to the expandedstated illustrated in FIG. 17E.

Graft tube 216 may be cut or otherwise manufactured to be the lengthrequired to extend along stent 110 starting at the exterior surface ofneck region 104 adjacent to first flared region 102, along the exteriorsurface of neck region 104 and second flared region 106, along theinterior surface of stent 110 and over the exterior surface of firstflared region 102 and neck region 104, terminating at the neck regionadjacent to second flared region 106. Alternatively, graft tube 216 maybe longer than desired and may be cut using well-known cuttingtechniques (e.g., micro-scissors, material cutting guillotine orlaser-cutting machine) to achieve the desired length after the approachdescribed with respect to FIGS. 17A-22D has been performed.

Referring now to FIG. 18A, to deposit graft tube 216 along the interiorof stent 110, graft tube 216 may be guided through the interior of stent110, as shown in FIG. 18A. To facilitate this process plunger 217, whichmay be any tool having a long shaft and a width or diameter less thanthe inner diameter of neck region 104 in the expanded state, may be usedto push graft tube 216 through the interior of stent 110. In thismanner, first graft portion 211 may extend along an exterior surface ofsecond flared region 106, curve around the end of second flared region106 and travel along the interior of stent 110 and out an opposing sideof stent 110.

Referring to FIG. 18B, to engage remaining portion of second graftportion 212 with the interior surface of stent 110, first mandrelportion 218 may be engaged with stent 110 and second graft portion 212.Having an end-shape formed to correspond to the interior of first flaredregion 102, first mandrel portion 218 may be gently advanced withinsecond end 215 of graft tube 216 and stent 110 until first mandrelportion 218 takes up nearly the entire space within first flared region102. This process may involve guiding first flared region 102 onto firstmandrel portion 218 while simultaneously guiding second end 215 of grafttube 216 over first mandrel portion 218 such that second end 215 of thegraft tube 216 extends along first mandrel portion 218 in a manner thatis tight fitting and free from wrinkles. When first flared region 102 isproperly mounted upon first mandrel portion 218, second end 215 of grafttube 216 will extend beyond the first flared region 102, as is shown inFIG. 18B. In this manner, second graft portion 212 may be partiallyengaged with stent 110 along an interior surface of stent 110.

Referring now to FIGS. 19A-19B, first mandrel portion 218 (FIG. 19A) andsecond mandrel portion 219 (FIG. 19B) are illustrated. As is illustratedin FIGS. 20A-20B, first mandrel portion 218 and second mandrel portion219 may be removably coupled to form mandrel assembly 220. Referring nowto FIG. 19A, a side view and head-on view of first mandrel portion 218is illustrated. First mandrel portion 218 may have first retentionportion 222 and first body portion 223, where first retention portion222 extends from first body portion 223. First retention portion 222 isdesigned to engage with stent-graft assembly 210 and have a similarshape as the first flared region and/or the neck region only withslightly smaller dimensions. First body portion 223 may have acylindrical shape. It is understood that first mandrel portion mayalternatively only have first retention portion 222. First mandrelportion 218 may have receiving portion 221 sized and configured toreceive protruding portion 228 of second mandrel portion 219. Receivingportion 221 may extend the entire length of first mandrel portion 218 ormay alternatively only extend a portion of first mandrel portion 218.

First mandrel portion 218 may also, optionally, have one or moreventilation holes 224 in first retention portion 222. Ventilation holes224 may extend through an exterior surface of first retention portion222 and may tunnel through the interior of first retention portion 222and first body portion 223 to ventilation inlet 225 which may extendthrough the surface of first body portion 223. Ventilation holes 224 arepreferably in the range of 0.1-2 mm in size, though it is understoodthat ventilation holes of different sizes may beneficial. Ventilationholes 224 may facilitate release of stent-graft assembly 210 after theheat treatment is applied, as explained below with respect to FIGS.22A-B. Specifically, after the encapsulated stent is tightly compressedagainst mandrel assembly 220, and the air between the encapsulated stentand mandrel assembly 220 is vacated, there may exist a suction forcemaking it difficult to remove the encapsulated stent. Ventilation inlet225 may permit air to flow through ventilation inlet to ventilationholes 224 to eliminate or reduce the suction effect. It is understoodthat multiple ventilation holes may communicate with one or moreventilation inlets.

Referring now to FIG. 19B, second mandrel portion 219 is illustrated.Second mandrel portion 219 may have second retention portion 226 andsecond body portion 227, where second retention portion 226 extends fromsecond body portion 227. Second retention portion 226 is designed toengage with stent-graft assembly 210 and may have a similar shape as thesecond flared region and/or the neck region only with slightly smallerdimensions. Second body portion 227 may have a cylindrical shape. It isunderstood that second mandrel portion may alternatively only havesecond retention portion 226.

Second mandrel portion 219 has protruding portion 228 sized and shapedto be received by receiving portion 221 of first mandrel portion 218.Protruding portion 228 may be, for example, a shaft that extends fromsecond retention portion 226. Protruding portion may be coaxial withsecond mandrel portion 219 and may be designed to extend part of thelength, the entire length or more than the length of first mandrelportion 218. Like first mandrel portion 218, second mandrel portion 219may, optionally, include one or more ventilation holes 229 and one ormore ventilation inlets 230.

Referring now to FIG. 20A, to constrain stent-graft assembly 210 onmandrel assembly 220, second mandrel portion 219 is removably coupledwith first mandrel portion 218 by engaging protruding portion 228 withreceiving portion 221. Second mandrel portion 219 may be gently advancedwithin second flared region 106 of stent-graft assembly 210 toward firstmandrel portion 218 until second mandrel portion 219 takes up nearly theentire space within second flared region 106 and protruding portion 228is fully received by receiving portion 221. In this manner, second graftportion 212 may be fully engaged with second flared region 106.

Protruding portion 228 may be designed to engage with receiving portion221 such that protruding portion 228 and engagement portion arereleasably locked together. Alternatively, protruding portion 228 may bedesign to friction fit within receiving portion 221. For example,protruding portion may be designed with a gradually increasing diameterthat may result in a friction fit with receiving portion 221. In thisexample, first mandrel portion 218 and second mandrel portion 219 may bereleased by forcibly pulling first mandrel portion 218 and secondmandrel portion 219 apart. It is understood that first mandrel portion218 and second mandrel portion 219 may be releasably locked together orotherwise friction fit together using various other well-knowntechniques. It is further understood that protruding portion 228 mayinstead extend from first mandrel portion 218 and receiving portion 221may instead be formed within second mandrel portion 219.

As is shown in FIG. 20A, after engaging second mandrel portion 219 withfirst mandrel portion 218, and thus constraining stent-graft assembly210 on mandrel assembly 220, third graft portion 213 may be separatedfrom the surface of first mandrel portion 218. For example, forceps maybe used to grasp second end 215 of graft tube 216 and gently pull secondend 215 over first flared region 102 and over neck region 104.Alternatively, other well-known techniques may be used for separatingthird graft portion 213 from first mandrel portion 218 and depositingthird graft portion 213 over first flared region 102 and neck region104.

Referring now to FIG. 20B, third graft portion 213 may gently becompressed against first flared region 102 and neck region 104 in amanner that reduces or eliminates wrinkles. For example, second end 215may be manually stretched using forceps toward neck region 104 andgently permitted to make contact with first flared region 102 and theportion of first graft portion 211 in contact with neck region 104.

By placing third graft portion 213 over first flared region 102 and neckregion 104, graft tube 216 will be deposited over stent 110 such thatgraft tube 216 covers stent 110 in the manner depicted in FIGS. 16A-16D.As is shown in FIG. 20C, depositing graft tube 216 over stent 110 in theforegoing manner results in three biocompatible layers of graft materialcovering neck region 104 of stent 110. Specifically, as is shown in FIG.20C, neck region 104 of stent 110 is covered on an interior surface bysecond graft portion 212 and is covered on an exterior surface by firstgraft portion 211 and third graft portion 213. In FIG. 20C, third graftportion 213 overlaps first graft portion 211 at neck region 104. As isshown in FIGS. 16B and 16D, first flared region 102 and second flaredregion 106 of stent 110 may only be covered by two layers ofbiocompatible material. In this manner, second graft portion 212 mayextend through a lumen of stent 110 through the first end of firstflared region 102, through neck region 104, and to the end of secondflared region 106; first graft portion 211 extends along an exterior ofsecond flared region 106 and neck region 104; and third graft portion213 extends along an exterior of first flared region 102 and neck region104, overlapping, at least partially, and joining with first graftportion 211.

It is understood that graft tube 216 may be deposited upon stent 110 toform stent-graft assembly 210 having the same three-layer structure atthe neck region 104 and two-layer structure at first flared region 102and second flared region 106 using different approaches than theapproach detailed in FIGS. 17A-20C. For example, graft tube 216 mayfirst be guided through the interior of stent 110. First end 214 andsecond end 215 may then be pulled in opposing directions while firstmandrel portion 218 and second mandrel portion 219 are gently insertedinto first flared region 102 and second flared region 106, respectively.First flared region and second flared region may be inserted until theyare sufficiently engaged and first mandrel portion 218 takes up nearlythe entire space within first flared region 102 and second mandrelportion 219 takes up nearly the entire space within second flared region106, thereby depositing and engaging second graft portion 212 with theinterior surface of stent 110. Next, second end 215 of graft tube 216may be separated from second mandrel portion 219, folded over secondflared region 106 and laid upon the outer surface of second flaredregion 106 and neck region 104, thereby depositing first portion overneck region 104 and second flared region 106. Finally, first end 214 maybe separated from first mandrel portion 218, folded over first flaredregion 102 and laid upon the outer surface of second flared region 106and neck region 104, thereby depositing third portion over second flaredregion 106 and neck region 104.

It is further understood that a three-layer structure may be depositedupon stent 110 in similar manner but resulting in the three-layerstructure occurring over first flared region 102, second flared region106, and/or neck region 104. Specifically, this alternative structuremay be achieved by depositing first end 214 of graft tube 216 at adifferent location along stent 110 and following the same generalapproach illustrated in FIG. 17A-20B. Depending on the length of grafttube 216, the resulting three-layer structure may span over some or allof first flared region 102, second flared region 106 and/or neck region104.

In another example, a similar stent-graft assembly may be generatedusing approaches similar to those described above but first depositingsecond end 215 over neck region 104, thereby placing third graft portion213 in direct contact with first flared region 102 and neck region 104.Second graft portion 212 may be deposited on the interior portion ofstent 110 but first end 214 will be wrapped around second flared region106 and rest upon first graft portion 211 in neck region 104. It isunderstood that this process may start with second mandrel portionentering the stent-graft assembly first.

In yet another example, a similar approach may be used to createstent-graft assembly having one region with four layers of biocompatiblematerial and other regions with two layers of biocompatible material.For example, a first graft portion may be deposited on first flaredregion 102 by positioning graft tube 216 over an exterior of firstflared region 102 such that first end 214 is placed over first flaredregion 102. Second end 215 may then be folded over flared region 102 andguided through the interior of first flared region 102, neck region 104and out second flared region 106 to deposit a second graft portion alongthe interior of stent 110. Second end 215 may then be folded over secondflared region 106 and guided over the exterior of stent 110 to firstflared region 102, thereby depositing a third graft portion over theexterior of second flared region 106, neck region 104 and first flaredregion 102. Finally, second end 215 may be folded over first flaredregion 102 and positioned within the interior portion of first flaredregion 102, thereby depositing a fourth graft portion over the interiorof first flared region 102. It is understood that a similar process maybe used to deposit four graft layers over second flared region 106 andtwo graft layers over neck region 104 and first flared region 102.

Referring now to FIGS. 21A-22D, to securely bond first graft portion211, second graft portion 212, and third graft portion 213 to stent 110and one another, pressure and heat may be applied to stent-graftassembly 210 to achieve sintering. As explained above, sintering resultsin strong, smooth, substantially continuous coating that covers theinner and outer surfaces of the stent. Sintering may be achieved byfirst covering stent-graft assembly 210 with a flexible sleeve (e.g.,flexible clamshell 231 shown in FIG. 21A), applying compressor 232(shown in FIG. 22A), and/or applying heat. In this manner, the firstgraft portion, second graft portion, and third graft portion may bebonded to one another through through-wall openings in stent 110.Accordingly, third graft portion and second graft portion may besintered together and joined.

The flexible sleeve may be tubular and also may be elastic andbiocompatible. For example, the flexible sleeve may be flexibleclamshell 231 illustrated in FIG. 21A. Flexible clamshell 231 ispreferably made from biocompatible silicone but may alternatively beother biocompatible materials having elastic properties. Flexibleclamshell 231 is hollow and may have a consistent thickness.Alternatively, flexible clamshell 231 may have varying thickness atdifferent points or in different sections. Flexible clamshell 231 hasfirst end 235 and second end 236 which may come together in a neutralposition. Alternatively, in a neutral position, there may exist alongitudinal void between first end 235 and second end 236. Flexibleclamshell 231 is designed such that first end 235 and second end 236 maybe separated by pulling first end 235 and second end 236 in opposingdirections.

Referring now to FIG. 21B, first end 235 and second end 236 may bepulled in opposing directions to create a longitudinal void such that,while stent-graft assembly 210 is positioned upon mandrel assembly 220,first end 235 and second end 236 may pulled over stent-graft assembly210. In this manner, flexible clamshell 231 either entirely or nearlyentirely covers stent-graft assembly 210. Flexible clamshell 231 may besized such that flexible clamshell 231 fits tightly over stent-graftassembly 210, as is illustrated in FIG. 21B. It is understood that athin metallic layer may be deposited over stent-graft assembly 210 priorto covering stent-graft assembly 210 in clamshell 231 such that the thinthe metallic layer may be sandwiched between stent-graft assembly 210and flexible clamshell 231 and may serve as a barrier betweenstent-graft assembly 210 and flexible clamshell 231. This barrier mayhelp prevent contaminants from clamshell 231 from transferring tostent-graft assembly 210. In one example, the thin metallic layer may bealuminum foil. In other examples, the thin metallic layer may betitanium, tantalum, or stainless steel, though it is understood thatother metals or alloys may be used. This process has been observed toenhance the compression and sintering process. Where the stent-graftassembly is wrapped with tape such as TFE or ePTFE tape, the tape maysimilarly prevent contaminants from transferring to the stent-graftassembly.

Flexible clamshell 231 may be sized such that when positioned overstent-graft assembly 210, flexible clamshell 231 applies a compressiveforce on stent-graft assembly 210. Flexible clamshell 231 may be sizedand configured to optimize the conformance of graft tube 216 to stent110 to minimize gaps between layers of graft tube 216 adjacent to strutsof stent 110. The degree of pressure that flexible clamshell 231 appliesto stent-graft assembly 210 may alter the inter nodal distance of thegraft material once sintered, described in more detail below. The extentto which flexible clamshell 231 covers, or does not cover, stent-graftassembly 210 also may alter the inter nodal distance. It is understoodthat inter nodal distance is related to tissue ingrowth and that thecompressive force applied by flexible clamshell 231 may be altered toachieve the desired inter nodal distance. Alternatively, any compressiveforce applied by flexible clamshell 231 may be negligible. Additionalcompression force on stent-graft assembly 210 may optionally be achievedby first wrapping stent-graft assembly 210 and/or flexible clamshell 231with tape such as TFE or ePTFE tape. For example, stent-graft assembly210 covered by flexible clamshell 231 may be placed in a helical windingwrapping machine which tension wraps the stent-graft assembly 210 andflexible clamshell 231 with at least one overlapping layer of tape,explained in more detail above.

Referring now to FIGS. 22A-22B, compressor 232 is illustrated.Compressor 232 has first half 233 and second half 234 and furtherincludes couplers 237 for removably coupling first half 233 to secondhalf 234. Couplers 237 may involve a screw with a locking nut or anyother well-known technique for removably locking two componentstogether. First half 233 and second half 234 may include receivingportions 238 that are sized and configured to receive couplers 237.First half 233 and second half 234 have an interior indentationconfigured to receive stent-graft assembly 210 covered by flexibleclamshell such that the interior indentation of each of first half 233and second half 234, when removably coupled together, has the shape ofstent-graft assembly 210 covered by flexible clamshell 231.Alternatively, the interior indentation of each of first half 233 andsecond half 234, when removably coupled together, has the shape of themandrel assembly 220, except with slightly larger radial dimensions.

First half 233 and second half 234 are rigid and preferably arestainless steel though it is understood that first half 233 and secondhalf 234 may be other rigid materials. First half 233 and second half234 may be designed such that first half 233 and second half 234 arepositioned a constant distance from stent-graft assembly 210 when firsthalf 233 and second half 234 are coupled together. Alternatively, thedistance from stent-graft assembly 210 or the mandrel assembly 220 mayvary at different regions of first half 233 and second half 234. Firsthalf 233 and second half 234 may be designed with a wall thicknessbetween an interior surface of first half 233 and second half 234 and anexterior surface of first half 233 and second half 234 that permits adesired degree of heat transfer. For example, first half 233 and secondhalf 234 may have a wall thickness that is thin to increase the amountof heat transfer to the stent-graft assembly. A thinner wall thicknessmay result in shorter sintering times, which may improve productionrates. Further, shorter sintering times lessen the effect of sinteringon the transformation temperatures (e.g., Austenitic Finish (Af)) of theNitinol frame.

Referring now to FIG. 22B, compressor 232 may be attached to clamshell231 covering stent-graft assembly 210 while stent-graft assembly ismounted upon mandrel assembly 220. Specifically, first half 233 may bepositioned over a first half portion of stent-graft assembly 210 andclamshell 231 and second half 234 may be positioned over a second halfportion of clamshell 231 and stent-graft assembly 210 such that firsthalf 233 and second half 234 entirely or nearly entirely cover flexibleclamshell 231. Once receiving portions 238 of first half 233 and secondhalf 234 are aligned, couplers 237 may be inserted into receivingportions 238 to removably couple first half 233 to second half 234 overclamshell 231. Couplers 237 may be tightened to increase the compressiveforce applied to stent-graft assembly 210. It is understood that thecompressive force applied by couplers 237 may alter the inter nodaldistance of the graft material once sintered. It is further understoodthat couplers 237 may be tightened to a certain degree to achieve adesired inter nodal distance.

Upon coupling first half 233 to second half 234 around flexibleclamshell 231, compressor 232 will have been positioned over flexibleclamshell 231, flexible clamshell 231 will have been positioned overstent-graft assembly 210, and stent-graft assembly 210 will have beenpositioned over mandrel assembly 220, as is illustrated in FIG. 22B,forming sintering assembly 239. Upon coupling first half 233 to secondhalf 234, compressor 232 applies a compressive force upon flexibleclamshell 231 and stent-graft assembly 210, thereby compressingstent-graft assembly 210 against mandrel assembly 220. Flexibleclamshell 231, due to its elastic properties, may facilitate evendistribution of compressive force against stent-graft assembly 210. Asis shown in FIG. 1, stent 110 may comprise a plurality of through-wallopenings. The force exerted by wrapping tape and/or compressor 232compresses stent-graft assembly 210 against mandrel assembly 220,thereby causing the graft layers to come into intimate contact throughinterstices of stent 110.

It may be desirable to vary the compressive force applied to stent-graftassembly 210 at certain points along stent-graft assembly 210. Forexample, flexible clamshell 231 may have varying thickness and/orlength, permitting compressor 232 to distribute varying degrees ofcompressive force upon stent-graft assembly according to the wallthickness and geometry of flexible clamshell 231. Additionally, thedistance from the interior walls to the surface of stent-graft assembly210 may vary at certain points along first half 233 and/or second half234. For example, a region of an interior wall of first half 233 havinga distance to stent-graft assembly 210 less than the rest of first half233 may apply a greater compression force on stent-graft assembly 210.Varying compressive force applied to stent-graft assembly 210 may reduceor increase conformance between first graft portion 211, second graftportion 212 and third graft portion 213. In an alternative embodiment,compressor 232 may be designed such that it only applies a compressionforce at neck region 104.

To form a monolithic layer of biocompatible material, first graftportion 211, second graft portion 212, and third graft portion 213 ofgraft tube 216 may be securely bonded together by applying heat tosintering assembly 239. For example, sintering assembly 239 may beheated by placing sintering assembly 239 into a radiant heat furnace,which may be preheated. Sintering may be performed as discussed in moredetail above. The heated assembly may then be allowed to cool for aperiod of time sufficient to permit manual handling of the assembly.After cooling, first half 233 and second half 234 of compressor 232 maybe decoupled and removed from flexible clamshell 231. Next, helicalwrap, if any, may be unwound and discarded. Flexible clamshell 231 maybe removed and encapsulated stent may then be concentrically rotatedabout the axis of the mandrel to release any adhesion between the secondgraft portion 212 and mandrel assembly 220. The encapsulated stent,still on mandrel assembly 220, may then be placed into a laser-trimmingfixture to trim excess graft materials away, in any. In addition, theencapsulated stent may be trimmed at various locations along the stentsuch as near one of the stent ends to permit coupling to deliverydevice.

The resulting structure shown in FIGS. 16A-16D and created using theapproach described with respect to FIGS. 17A-22B is beneficial in thatbiocompatible material does not terminate at either end of stent-graftassembly 210 but instead terminates at neck region 104 of stent 110. Theinventors have discovered that biocompatible material that extendsbeyond a stent at either end is known to result in thrombus formationwhen implanted and could also cause interference with attachment to adelivery catheter. The reduction in graft overhang at the edges alsoimproves fluid dynamics at the inlet and outlet of the encapsulatedstent. As an added benefit, the resulting triple-layer structure at neckregion 104 has been observed by the inventors to further inhibit tissueingrowth. It is understood that the foregoing method described withrespect to FIGS. 17A-22B helps prevent gaps between biocompatiblelayers, which might result in extensive tissue ingrowth, and also helpsminimize microscopic surface thinning defects (MSTDs), which couldresult in attracting platelet thrombi. Applicants understand that theapproach described with respect to FIGS. 17A-22B provides a high yieldand highly reproducible manufacturing process.

Applicants have further observed that heating sintering assembly 239including a flexible clamshell comprised of silicone, as describedherein, results in small fragments and/or molecular portions of siliconebeing deposited upon graft tube 216 and/or becoming impregnated in grafttube 216. It has been observed by the Applicant that the fragmentsand/or molecular portions of silicone deposited on and/or impregnated ingraft tube 216 may further reduce tissue ingrowth when the encapsulatedstent is implanted.

Referring now to FIGS. 23A-C the encapsulated stent generated using theapproach described above with respect to FIGS. 17A-22B is shownimplanted in the atrial septum of an animal subject. Specifically, FIG.23A shows the first flared region of the encapsulated stent, FIG. 23Bshows the neck region of the encapsulated stent and the second flaredregion, and FIG. 23C illustrates the second flared region of theencapsulated stent.

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. For example, the assembly mandrels described herein mayinclude additional or fewer components of various sizes and composition.Furthermore, while stent encapsulation is described herein, it isunderstood that the same procedures may be used to encapsulate any otherbio-compatible material. The appended claims are intended to cover allsuch changes and modifications that fall within the true spirit andscope of the invention.

What is claimed is:
 1. A method for making an encapsulated stent-graft,the method comprising: compressing a stent comprising a first flaredregion, a second flared region, and a neck region situated between thefirst flared region and the second flared region, into a compressedstate; positioning the second flared region and the neck region within agraft tube comprising a first end and a second end; releasing the secondflared region to an expanded state within the graft tube therebydepositing a first layer of graft material over the neck region and thesecond flared region; releasing the first flared region to expand to theexpanded state; guiding the second end of the graft tube through aninterior portion of the stent such that the second end of the graft tubeextends beyond the first flared region, thereby depositing a secondlayer of graft material along the interior portion; selecting a mandrelcomprising a first portion comprising a first mandrel end that isremovably coupled to a second portion comprising a second mandrel end;guiding the first flared region onto the first portion of the mandrelwhile guiding the second end of the graft tube over the first portion ofthe mandrel such that the second end of the graft tube extends beyondthe first flared region; coupling the second mandrel end of the secondportion of the mandrel to the first mandrel end of the first portion ofthe mandrel; and guiding the second end of the graft tube over the firstflared region and over the neck region, thereby depositing a third layerof graft material over the first flared region and the neck region, thestent and graft tube forming a stent-graft assembly comprising threelayers of graft material at the neck region and two layers of graftmaterial at the first flared region and the second flared region.
 2. Themethod of claim 1, wherein the first flared region has a diameter thatis larger than a diameter of the second flared region and the secondflared region has a diameter that is larger than the neck region.
 3. Themethod of claim 1, further comprising: selecting a flexible sleevehaving a first sleeve end and a second sleeve end and a shape configuredto receive the stent-graft assembly; flexing the flexible sleeve suchthat the first sleeve end is separated from the second sleeve end; andpositioning the flexible sleeve over the stent-graft assembly while thestent-graft assembly is positioned on the mandrel.
 4. The method ofclaim 3, wherein selecting the flexible sleeve comprises selecting aflexible sleeve comprised of silicone.
 5. The method of claim 3, whereinselecting the flexible sleeve comprises selecting a flexible sleevehaving a wall thickness that is constant.
 6. The method of claim 3,wherein selecting the flexible sleeve comprises selecting a flexiblesleeve having a varying thickness.
 7. The method of claim 3, whereinselecting a flexible sleeve comprises selecting a flexible sleeve sizedand configured to reduce an inter nodal distance within the graft tube.8. The method of claim 3, further comprising: selecting a compressorcomprising a first half that is removably coupled to a second half, thefirst half and the second half each comprising an interior surfacehaving an indentation sized and configured to receive the flexiblesleeve covering the stent-graft assembly; positioning the first half andthe second half of the compressor around the flexible sleeve coveringthe stent-graft assembly; and coupling the first half of the compressorto the second half of the compressor while the first half of thecompressor and the second half of the compressor are positioned aroundthe flexible sleeve covering the stent-graft assembly, wherein thecompressor, the flexible sleeve, the stent-graft assembly, and themandrel form a sintering assembly.
 9. The method of claim 8, whereinselecting a compressor comprises selecting a compressor comprised ofstainless steel.
 10. The method of claim 8, wherein selecting acompressor comprises selecting a compressor having a thickness thatfacilities heat-transfer to the stent-graft assembly.
 11. The method ofclaim 8, wherein selecting a compressor comprises selecting a compressorthat applies a consistent compression force to the stent-graft assembly.12. The method of claim 8, wherein selecting a compressor comprisesselecting a compressor that applies a compression force to stent-graftassembly that varies.
 13. The method of claim 8, wherein selecting acompressor comprises selecting a compressor sized and configured toreduce an inter nodal distance within the graft tube.
 14. The method ofclaim 8, wherein coupling the first half of the compressor to the secondhalf of the compressor applies a compression force to the flexiblesleeve, thereby compressing the stent-graft assembly against themandrel.
 15. The method of claim 14, wherein the flexible sleevefacilitates even distribution of the compression force applied to thestent-graft assembly by the compressor.
 16. The method of claim 8,further comprising, heating the sintering assembly to cause the firstlayer, the second layer, and the third layer of graft material to becomesintered together to form a monolithic layer of graft material, therebyforming the encapsulated stent-graft.
 17. The method of claim 16,wherein the stent comprises through-wall openings and heating thesintering assembly causes the first layer, second layer, and third layerof graft material to bond to one another through the through-wallopenings.
 18. The method of claim 16, wherein the flexible sleeve issilicone and heating the sintering assembly causes the flexible sleeveto deposit silicone fragments into the stent-graft assembly.
 19. Themethod of claim 8, further comprising winding a layer of tape over theflexible sleeve to compress the stent-graft assembly against themandrel.
 20. A method for making an encapsulated stent-graft, the methodcomprising: selecting a stent comprising a first flared region, a secondflared region, and a neck region disposed between the first flaredregion and the second flared region; selecting a graft tube comprising afirst end and a second end; positioning the second flared region and theneck region within the first end of the graft tube, thereby depositing afirst layer of graft material over the neck region and the second flaredregion; guiding the second end of the graft tube into the second flaredregion, through an interior portion of the stent, and out the firstflared region, thereby depositing a second layer of graft material alongthe interior portion of the stent; and guiding the second end of thegraft tube over the first flared region and over the neck region of thestent, thereby depositing a third layer of graft material over the firstflared region and the neck region, the stent and graft tube forming astent-graft assembly.
 21. The method of claim 20, further comprising:selecting a mandrel comprising a first portion comprising a firstmandrel end and a second portion comprising a second mandrel end that isremovably coupled to the first mandrel end; guiding the first flaredregion onto the first portion of the mandrel while guiding the secondend of the graft tube over the first portion of the mandrel such thatthe second end of the graft tube extends beyond the first flared region;coupling the second mandrel end of the second portion of the mandrel tothe first mandrel end of the first portion of the mandrel; selecting aflexible sleeve having a first sleeve end and a second sleeve end and ashape configured to receive the stent-graft assembly; flexing theflexible sleeve such that the first sleeve end is separated from thesecond sleeve end; and positioning the flexible sleeve over thestent-graft assembly while the stent-graft assembly is positioned on themandrel.
 22. The method of claim 21, wherein selecting a flexible sleevecomprises selecting a flexible sleeve sized and configured to reduce aninter nodal distance within the graft tube.
 23. The method of claim 21,further comprising: selecting a compressor comprising a first half thatis removably coupled to a second half, the first half and the secondhalf each comprising an interior surface having an indentation sized andconfigured to receive the flexible sleeve covering the stent-graftassembly; positioning the first half and the second half of thecompressor around the flexible sleeve covering the stent-graft assembly;and coupling the first half of the compressor to the second half of thecompressor while the first half of the compressor and the second half ofthe compressor are positioned around the flexible sleeve covering thestent-graft assembly, wherein the compressor, the flexible sleeve, thestent-graft assembly, and the mandrel form a sintering assembly.
 24. Themethod of claim 23, wherein selecting a compressor comprises selecting acompressor having a thickness that facilities heat-transfer to thestent-graft assembly.
 25. The method of claim 23, wherein selecting acompressor comprises selecting a compressor sized and configured toreduce an inter nodal distance within the graft tube.
 26. The method ofclaim 23, wherein coupling the first half of the compressor to thesecond half of the compressor applies a compression force to theflexible sleeve, thereby compressing the stent-graft assembly againstthe mandrel.
 27. The method of claim 26, wherein the flexible sleevefacilitates even distribution of the compression force applied to thestent-graft assembly by the compressor.
 28. The method of claim 23,further comprising, heating the sintering assembly to cause the firstlayer, the second layer, and the third layer of graft material to becomesintered together to form a monolithic layer of graft material, therebyforming the encapsulated stent-graft, wherein the stent comprisesthrough-wall openings and heating the sintering assembly causes thefirst layer, second layer, and third layer of graft material to bond toone another through the through-wall openings.
 29. The method of claim28, wherein the flexible sleeve is silicone and heating the sinteringassembly causes the flexible sleeve to deposit silicone fragments intothe stent-graft assembly.